Police believe that missing college student Mollie Tibbetts is still alive and being held hostage by her abductor - who may have attended the candlelit vigil in her honor, a source claims.

The source, who is close to the FBI investigation into Tibbetts' disappearance, told Radar her kidnapper may have even assisted in the search for the missing 20-year-old.

They said the suspect was 'hiding in plain sight' and has been 'closely follow[ing] the case.'

University of Iowa student Tibbetts was last seen going for a run in Brooklyn, Iowa, on July 18, and two weeks later, more than 200 people gathered at the RiverLoop Amphitheatre in Waterloo for a candlelit vigil in her honor.

Police believe that missing college student Mollie Tibbetts is still alive and being held hostage by her abductor

Now the law enforcement source has revealed that investigators believe that her kidnapper may have been among her distraught family and friends at the event.

'There is reason to believe the person responsible for Mollie's disappearance attended a vigil and has continued to closely follow the case,' they said.

They said that authorities are tightening the net around the suspect and are looking at single, divorced, and widowed men around Brooklyn, Iowa. They are also examining Tibbetts' 'digital footprint', including date from her Fitbit and cell, to track her down.

Tibbetts' father, Rob Tibbetts, (right) agrees and believes that his daughter was taken by someone she knows, while her brother Scott (left) is hopeful she's still alive

The website includes a map (pictured above) that pinpoints the five spots investigators are focusing on. Police have not indicated why they are honing in on these locations

But there was some hope for the family, as the source said that investigators believe she is still alive.

'There is reason to believe Mollie is still being held captive and whoever this person is, agents from the FBI and local law enforcement agencies are closing in,' they said.

Tibbetts' father, Rob Tibbetts, agrees and believes that his daughter was taken by someone she knows.

'I do believe Mollie is with someone who she knows, probably someone who cares about her,' he said. But that relationship was misguided, misinterpreted and went wrong, and I think they're in a place with Mollie and don't know how to get themselves out of this horrible situation.'

A vigil took place in Waterloo, Iowa, where parents pleaded for missing children including Mollie Tibbets, Elizabeth Collins, Lyric cook and Jake Watson to be safely returned home.

The missing student's brother Scott is also sure his sister is still alive.

'I do believe that she's still alive, and the reason I think that is because I know her and know her strong she is. I know the sort of attitude she had and she would never give up,' he said on All Rise with Dylan Howard. 'I'm still hoping for the best.'

Scott refused to talk about who he thinks may have taken his sister and also declined to speculate about why police had searched the farm of a local pig farmer who had multiple arrests for stalking. He has already been interviewed twice by police.

Police have also declined to explain their focus on the pig farm and have given very few details of their investigation.

Mollie was staying alone in the home she shared with her boyfriend Jack Dalton (above) in Brooklyn when she vanished after going for an evening run on July 18. He's been cleared as a suspect

'They haven't told us a whole lot about that,' Scott said of the FBI and police's investigation. 'We wouldn't share too much about it, we wouldn't want to speculate a whole lot.

'I'm confident in the authorities and I'll let them bring the details to light.'

Host Howard also raised a report from a neighbor who say a black SUV circling the area that Tibbetts disappeared in.

She had been staying at the home of her boyfriend Dalton Jack, who has been ruled out as a suspect.

He appears to have been the last person to have communicated with her, receiving a Snapchat message from Tibbetts on the night she disappeared. He opened it at around 10pm on July 18, although it may have been sent earlier that evening.

Tibbetts was last seen at 7.30pm that night.

Her brother said he hadn't seen the message and had not interest in seeing his sister's final words.

When asked why, he told Howard: 'I'm sure they were just talking. I'm sure it was just regular conversation. It wasn't sent to me so I don't care to see it.'

The search for Tibbetts has now zeroed in on five areas, including a truck stop and car wash, in the rural Iowa town where she vanished from a month ago.

Investigators searching for the 20-year-old launched a new website on Monday to generate tips from potential witnesses who were near those specific areas in Brooklyn around the time she was last seen on July 18.

The website, FindingMollie.Iowa.gov, includes an interactive map that pinpoints the five spots investigators are focusing on.

Among the locations that they are seeking tips from is a TA truck stop along the Interstate-80 and a car wash near the center of the city.

Other locations are two pieces of rural land on the outskirts of Brooklyn and the area near the home where she had been staying with her boyfriend Dalton Jack.

'Law enforcement is currently seeking additional witnesses and wants to speak to anyone who was in the areas indicated below on July 18, 2018 between the hours of 5pm and 10pm,' the website states.

Investigators revealed on Monday they were focusing on getting tips from people at five locations, including this TA truck stop along the Interstate-80

This car wash near the center of the city is among the five locations investigators are seeking tips from

Police have not indicated why they are honing in on these locations.

Iowa Division of Criminal Investigation assistant director Mitch Mortvedt says investigators are considering all scenarios but that it's 'possible that Mollie has come into contact with someone who has caused her harm'.

He asked the public to report information about anyone who has recently displayed odd behaviors.

'Often, someone in the community will unknowingly be associated with the offender, and may be in a position to observe behavioral changes in that person,' he said.

'They will recognize the change and may even question them about it, but will not relate the change to that person's involvement in a crime.'

Some of the changes he urged people to consider include: changes in normal routine, a vehicle being unexpectedly taken to a repair shop or sold, intensive cleaning of a vehicle, altering of physical appearance, unexplained injuries and interest in the investigation.

Police are seeking tips from the public who were in the vicinity of the home (above) where Mollie had been staying alone the night she disappeared

Farm land close to Big Bear Creek - a waterway that runs through Brooklyn - is also one of the areas

Mollie was staying alone in the home she shared with her boyfriend, his brother and his brother's fiancee when she vanished after going out for an evening run on July 18.

Her disappearance has sparked an enormous search effort involving local, state and federal authorities and volunteers.

The reward fund offered for her safe return has grown to nearly $316,000.

She was last seen alive, it is thought, by Devin Riley who lives on the other side of town and saw her jog past his home. He contacted police when he heard she was missing from the news.

Mollie's boyfriend says he received a Snapchat message from Tibbetts after she would have returned from her run.

When Mollie went jogging, she had her phone, FitBit and her arm band. None of those items have been found.

Jack's brother, Blake, told Fox News there were no signs of struggle at the home, adding that Tibbetts is 'small, but she would have done something' if she had been attacked.