Zigzagging through Karachi’s main road, Layla Gulnaz*, 46, is on a mission. Beneath a sweltering sun, she goes from one car to the next, peering intently at the backseat passengers as she asks for spare change. She approaches a black car with a family of five inside.

As the father reaches for change, Gulnaz quickly scans the faces of the three children in the back. To buy time, she makes small talk, but the man passes her a few rupees and hastily rolls up the car window.

“They think we’re freaks,” she says, rolling her eyes. “That we steal children because we can’t have our own. But here we are, doing the exact opposite.” Gulnaz pulls out a crumpled photo from her purse and sighs; the missing child she has spent all afternoon searching for – 13-year-old Asma Razzak – is nowhere to be found.

Gulnaz is one of Pakistan’s estimated 500,000 transgender people, who are largely shunned and driven to the dangerous margins of Karachi life. Many end up working in vulnerable industries such as the sex trade.

Gulnaz is also on the frontline of Pakistan’s battle to overcome an epidemic of child disappearances linked to slavery, exploitation and murder.

According to NGO Sahil, in a survey of 85 national and regional newspapers, 1,064 child abduction cases were reported, of which 79% were girls and 21% boys. This is part of a wider story of children going missing across Pakistan; exploited, abused, sold into forced marriage or slavery. In its latest report, Sahil found the main reasons for abduction were trafficking, begging, sex work and bonded labour in brick kilns.

For years this issue has been largely ignored, but in recent weeks the desperate tale of Pakistan’s missing children has become a national scandal. The discovery of four children’s bodies in shallow graves and on rubbish dumps in the Kasur district of Punjab, south of Lahore, in September sparked demonstrations over police inaction. Cars were burned and the local police station was pelted with stones. The prime minister, Imran Khan, stepped in, promising that the police would be held to account, and unveiling an app to track children from the moment they vanish.

Zubaida Shaheen holds up a photo of her daughter, Mursaleen Khizer, six, who has been missing for two years. Photograph: Mohammad Ali Addarsh/The Guardian

Kasur was already notorious across Pakistan for child murder. In January 2018 seven-year-old Zainab Ansari went missing while walking the short distance from her house to Qur’an school.

Four days later, after her family tracked down CCTV footage, reportedly with little help from the police, her body was found on a rubbish dump. She had been raped and strangled. Her disappearance was the latest in a long line of local children to go missing. Imran Ali, 24, was convicted of Zainab’s killing, and police investigators also matched his DNA with seven other girls’ bodies.

In Karachi, a low-tech revolution, led by society’s outcasts, is leading where police have failed.

Gulnaz is part of a team put together by human rights activist Muhammad Ali. In 2007, Ali founded Roshni Helpline, Pakistan’s first hotline for missing children, which uses a complex system of volunteer informants. This includes transgender sex workers, neighbours, blacksmiths, street vendors and all those aware of who is coming and going through the underground routes of trafficking. Together, they claim to have helped locate more than 5,000 of Karachi’s missing children and reunited them with their families.

Muhammad Ali, founder of Roshni Helpline, in his office. Photograph: Mohammad Ali Addarsh/The Guardian

Living on the margins gives Gulnaz a strong empathy with the families who are losing children. “They usually belong to poorer families, so the police don’t take their cases seriously,” she says. “Security is a luxury not everyone here can afford.”

Sitting on a swivel chair behind a mahogany desk stacked with case files of missing children, Ali says the reasons for abductions vary.

“Newborns until the age of three are mainly kidnapped for false adoption while children between three and 10 are more vulnerable to sexual exploitation, [forced begging] and ransom. From 10 onwards, we also find runaway cases due to domestic abuse or the threat of child marriage.”

The walls of his small office are plastered with cut-out clippings of missing children – small, black-and-white printed faces stare back, frozen in time. Mursaleen Khizer, six, missing since 26 August 2017. Aisha Zafar, 12, missing since 1 September 2018. Tahir Khan, 16, missing since 6 March 2019 – the list is long. Missing children ads are as regular as crossword puzzles in Urdu newspapers.

“The idea to involve transgender [people] came because they have good connections in the city,” says Ali. It was the ability of the khawaja sira – as trans people are commonly known – to move through the margins of society, dangerous places that traditional authorities have no access to, that led him to approach them. “It seemed obvious,” he says. “They would be able to help us.”

Typically cast out by their families, Pakistan’s transgender community knows all too well what estrangement feels like. “We’ve also been abandoned,” Gulnaz laments. “We understand the pain of separation so reuniting these children with their families makes us feel good for a while.”

Gulnaz moved to Karachi at the age of 15 after being disowned by her family. “I came here to find a job, but found only one difficulty after another.” To survive, she juggles her time between begging and dancing. “I take work wherever I can find it,” she explains.

On a warm afternoon, Ali and his team gather around for their weekly meeting. Shehla Khan*, 40, has been working with Roshni for the past four years and manages a group of 50 other transgender volunteers. Today they are being briefed by the case management team on children who have recently gone missing in the area. The volunteers listen intently as they are equipped with photos and information about each child.

Ali’s team carefully maps out an area where a child has gone missing. Colour-coded drawing pins determine key entryways and exits to ensure they are carefully watched. Volunteers are told to scout vulnerable areas such as Mobina Town, Gulshan-e-Iqbal and Jamshed Town, where they must remain particularly vigilant.

“I was recently tipped off on the whereabouts of a kidnapped girl, who was being exploited at an unknown house,” says Khan. “I immediately informed Roshni, who, together with the police, were able to track down the location. After carrying out a raid, they not only found the girl but three others who were being kept in the basement.”

Shehla is also a guru, a guardian of younger transgender women, many of whom come to her after being abandoned by their families. Shunned by mainstream society, Pakistan’s transgender community is often subjected to violence and hostility. In the past three years, 58 have been murdered in the Khyber Pakhtunkhwa province alone.

Ali’s persistence has taken his fight all the way to Pakistan’s supreme court, where he is now pushing for a law that would ensure the police act promptly when a child goes missing. “Even 24 hours is too long to wait,” he says. “It has to be the moment a child goes missing.”

Later that evening Gulnaz is back on the road. Asma Razzak has yet to be found, and Gulnaz isn’t giving up. The call to prayer rings out from a minaret and worshippers start to descend on a nearby mosque. “It’s so easy to get overlooked in this big city. But one glance is all it takes,” Gulnaz says determinedly. “If you’re in the right place at the right time, a glance can save someone’s life.”

*Names changed to protect identities