Malaysia Airlines flight MH370 disappeared on 8 March 2014, mid-flight from Kuala Lumpur to Beijing with 239 people onboard. Two and a half years later, despite the multi-million-dollar investment and efforts of three countries, the plane has yet to be found.

There have been traces. Two pieces of aircraft debris found washed up on remote beaches of the Indian Ocean have been confirmed as being from MH370, with the latest – an outboard flap from Pemba Island – discovered only this month. Four more pieces are almost certain to be from the lost plane.

Earlier this month, the Malaysian transport minister, Datuk Seri Liow Tiong Lai, said that 22 potential pieces of aircraft debris had been found so far, along the coastlines of South Africa, Mozambique, Mauritius and Tanzania. Fourteen of these fragments have been found by one man, Blaine Alan Gibson, the result of an independent, self-funded investigation he began 18 months ago. Several are under investigation or awaiting pickup by authorities, but one – a horizontal stabiliser, stencilled with the words “NO STEP”, which Gibson found on a sandbank in Mozambique in late February – is almost certainly from MH370.

Gibson is most often described as a Seattle-based lawyer. He prefers “adventurer”. He can speak six languages, and has said it is his dream to go to every country in the world. Mozambique, where he was technically on holiday, was number 177 on the list. “I’ve stopped at that because I’m trying to find the plane,” he says. “There are other places I want to go, but the plane isn’t there.”

Wearing hiking boots, head-to-toe khaki tones and a slouch hat – a new acquisition – atop a thatch of hair, he dresses as if he is courting comparisons with Indiana Jones (a Google search reveals that the strategy has worked).

Volunteers gather debris found on Réunion island, in August 2015. Photograph: Arnaud Andrieu/EPA

The look, topped off with a badge reading “The search for MH370: Keep it on”, is striking when we meet in a bookshop-cum-cafe in an inner-city Sydney suburb, but Gibson has been living out of his suitcase for a while. He passed his bar exams in 1993, but has rarely practised (his father, Phil S Gibson, served as chief justice of the California supreme court from 1940 to 1964). It’s been decades, in fact, since his life has conformed to a standard nine-to-five.

Now in his late 50s, he is not married. He does not have children. He has an apartment in Seattle, but no car any more. “Everything I spend is on travel, and I’ve always liked the travel to have a purpose.” In the past, that has meant being present for significant political or historical events – he was in Red Square “when the red flag came down” on the last day of the Soviet Union. Or it can be “to solve some mystery”, such as his trips to Guatemala and Belize, to uncover the fate of the Mayan civilisation, or Siberia, to learn about the Tunguska meteorite, thought to have created a blast as powerful as 1,000 Hiroshimas in 1908.

MH370 is his latest mission and, he says, his most successful. “This one is special because the others have been for history and interest, and this one is for the families, because it means so much to them to get some traces of answers.”

When the plane disappeared, he was on an infrequent trip back to the US, tasked with selling the family home in California that – with his parents both gone, and his constant globetrotting – had become a burden. “I sat glued to the TV more than I normally would because I had to be there to sign documents, do inspections, sort through all my family memories.”

Plane debris from MH370 found in South Africa. Photograph: EPA

Gibson spent much of the next year in Laos, helping friends set up a karaoke bar, but maintained an active interest in the search in discussion groups on Facebook. One such group, MH370 In Search of the Truth, now has more than 3,600 active members; Gibson was one of the first.

He flew to Kuala Lumpur for the public service marking the first anniversary of the plane’s disappearance, and was moved by a “heart-rending” speech given by Grace Subathirai Nathan, whose mother was on the plane and who continues to speak on behalf of the families of missing passengers.

“That made me think this is something that maybe I can do – to do what I love doing anyhow, travel and solving mysteries, but also have a reason for it.” He is now friends with Nathan, and many other MH370 families.

First, he flew to Myanmar and Cambodia, not far from Laos, to explore the possibility that the plane had flown north. Then he interviewed local people in the Maldives who had reported seeing a jet plane the morning MH370 disappeared (their accounts contradicted satellite data and were set aside). In July 2015, a six-foot flaperon wing was found on Réunion island, east of Madagascar – and Gibson’s search area was narrowed down.

Since finding the horizontal stabiliser panel in February, he seems to have tracked down potential pieces of MH370 faster than investigators can assess them, or even pick them up – he says six items have been awaiting collection in Madagascar by Malaysian authorities for more than three months.

He has come to Sydney from Canberra, where he handed six further fragments found in Madagascar over to Australian investigators for analysis. Two apparently showed signs of charring, raising the possibility there was a fire onboard the plane before it crashed. (Two weeks later, the Australian Transport Safety Bureau (ATSB) found the dark colouration was not caused by exposure or fire, but did not rule out a possible link to MH370.)

An Australian investigators’ map showing the Indian Ocean search area in 2015.

Even allowing for misses, Gibson’s successes have been remarkable, especially given his lack of professional expertise and resources. He has no prior aviation experience, although he says he is learning. “I know now what pieces of a plane look like. I’ve probably held in my hands more pieces of Malaysia 370 since it crashed than anyone alive.”

His methods are simple: he looks on beaches, he puts the word out with locals, he checks shacks, because large pieces of metal are valuable construction materials. It’s slow and labour-intensive in comparison with the initial search effort in March 2014, two weeks after the plane disappeared, when 22 military aircraft and 19 ships from eight countries covered areas of more than 4.6m sq km.

Although Malaysia holds overall responsibility for the accident investigation, the ATSB has led the underwater search since April 2014. When Gibson finds debris, he notifies Australian and Malaysian authorities, although it is Malaysia’s responsibility to retrieve potential evidence.

The official search of a 120,000 sq km arc of ocean, determined from satellite data and drift modelling as the most likely site of the wreck, is expected to be completed in December. With less than 10,000 sq km to go, it seems increasingly likely it will be unsuccessful. But Gibson rejects the idea that he is doing a better job than the ATSB. “They’re out there in 20-metre waves, miserable, cold, trying to find something 6,000-metres deep. I’m walking along a beach picking things up after the ocean has done its work,” he says. “It’s not fair to compare the two of us ... and what they have the possibility of finding, which is the black boxes – I mean, that’s the holy grail.”

In early September, he and relatives of the missing passengers met the crew of the Fugro Equator, one of the search vessels, in port in Fremantle, Western Australia. “There were choked-back emotions and tears from these tough guys out on the boat,” says Gibson. “They really care, they’re really dedicated, and I hate to see the media trash them, trash the ATSB ... they really want to find this plane.” For the ATSB’s part, a spokesman says Gibson’s efforts have reinvigorated public interest in the search, and led to more members of the public coming forward with items.

Gibson is less effusive about the Malaysian authorities, who he has found to be slow to retrieve potential evidence. But “more frustrating” are people, particularly journalists, who cherrypick evidence to suit their “pet theories” – of which there are plenty. “Sometimes it seems to me that I’m the only person who doesn’t know where the plane is and what happened to it,” he says.

He singles out an Australian primetime current affairs programme that claimed in its “special investigation” that the plane’s fuselage was intact under water, even though he believes he has found debris from the cabin interior. “I was holding pieces – you’ve seen the pictures. I’m not under 600 atmospheres of pressure, it’s not dark, I’m breathing normally. I wasn’t underwater,” he says.

Gibson, second from left, with relatives of passengers on MH370 including Grace Subathirai Nathan, second from right, after a meeting in Canberra, Australia. Photograph: Mark Graham/AFP/Getty Images

Worse still, he says, are theories implicating the captain of MH370, Zaharie Ahmad Shah. New York magazine reported in July that a route plotted on his home flight simulator “closely matched” that taken by the plane. The story was authored by Jeff Wise, a high-profile but controversial commentator on the search for MH370 who has posited a number of theories, including that it was hijacked and flown to Kazakhstan on Vladimir Putin’s instruction. But, says Gibson, even if it wasn’t a stretch to interpret a simulated route as evidence of planning, to say the two routes “closely matched” is just not true.

The evidence thus far points to a high-speed impact that shattered the plane, including the main cabin – inconsistent with a controlled glide by a suicidal pilot.

“There is nothing in the background of this pilot to indicate that he would want to end his life or everybody else’s – nothing,” he says. “The only evidence against him is the absence of any other explanation. That’s not enough.”

Gibson says he has been “trolled, attacked and slandered” by an “online army of armchair assassins”, who have accused him of having reported planted debris, even planting it himself. A cyber-attack on The Hunt for MH370 website, after it published his report on the possible sighting in the Maldives, seemed professional, he says, although he does not know if his detractors are paid to discredit him, or “just mean people”.

He insists that he is driven only by the desire to find out what happened to the plane. “The problem with Malaysia 370 is there are too many theories and not enough evidence. I can tell you what we do know. The plane crashed in the Indian Ocean, somewhere south of the equator and north of 39 degrees south [latitude] – probably more likely north of 34 degrees south.

“It did not crash in the Gulf of Thailand. It did not crash in the Bay of Bengal. It is not buried in the sand of Kazakhstan. It is not south of 40 degrees, because then debris would have gone to Australia and Tasmania – and it wasn’t abducted by aliens.” He says it is possible that there was an emergency that crew members tried and failed to respond to. It is also possible that the plane was hijacked.

There is no neat narrative, which, he accepts, people find difficult. But speculation at least fuels the search.

“As long as the interest remains in solving this mystery, I am content, because we need the search on until we do [solve it],” says Gibson. “What bothers me are the easy answers that cause us to say: ‘Mystery solved, sweep it under the rug for ever, pin it on the pilot.’ I don’t like the easy answers.”

Gibson is hopeful the search will continue, in some form, beyond December. His investigation continues: “I’m hooked now.” However, he believes governments, airlines and manufacturers – even those not directly linked – should play their part.

“We have to solve this mystery. It’s not just for the families, it’s for the flying public, who need to be sure what happened never happens again. We need to know that when we get on a plane, yeah, it may crash, things happen. But it’s not going to just disappear.”