The family of missing Isle of Wight boy Damien Nettles is offering a reward to help catch those responsible for his suspected murder.
The teenager was last seen after a night out in West Cowes on 2 November 1996 when he was 16.
The Nettles family hopes to offer £10,000 in a bid to solve the case.
Valerie Nettles, Damien's mother, who believes there are "answers to be found" on the island, hopes the reward will encourage people to come forward.
Mrs Nettles, who now lives in Texas, said: "I've always had a gut feeling that something bad happened to Damien. I want to know why they did it and where they put him.
"He was 16 when he went out in Cowes with friends. I thought it was one of the safest places on earth.
'Worst possible torture'
"I just want to know where they put his body. I don't believe he fell in the sea and floated away.
"We seem to be getting a story over and over again which has the same theme to it and the same characters."
Mrs Nettles said the family had wanted to offer a reward in conjunction with Hampshire Constabulary for some years, but had been dissuaded from doing so by the force.
The reward will be paid for information which leads to those responsible for Damien's suspected murder being convicted and her son's remains found.
Mrs Nettles, who moved to the US to be closer to members of her family, said: "Not knowing is the worst possible torture. We want to know what happened.
"I can't remember what kind of person I was before all of this. I can't not look for my child."
Mrs Nettles thanked those who helped raise more than £500 towards the reward within the first four hours of the family's appeal.
"In the eventuality we are unsuccessful getting the required results, we will distribute any funds to UK based charities," she added.
The last confirmed sighting of Damien was on CCTV at Yorkie's fish and chip shop in Cowes High Street at about 23:45 GMT.
In 2010, Damien's case was changed by the police from that of a missing person to a suspected murder investigation.
In May last year, specialist teams using rafts combed the water and reed beds at Dodnor Nature Reserve, near Newport, but failed to find his body.
No evidence was found during a police search of a property at Marsh Road, in Gurnard, in November 2011.
Earlier this month police said no further action would be taken against four men arrested in connection with Damien's disappearance in May 2011.
A 38-year-old man from Ryde, Isle of Wight, was re-bailed until 7 March.
In January a 35-year-old woman and a 44-year-old man, both from Cowes, who were arrested in November 2011, had their bail extended until 7 March.
Senior investigating officer Supt David Powell, of Hampshire Constabulary, said: "I do not rule out any options completely in our investigation to find out what happened to Damien Nettles.
"However, at this time, a dedicated team of officers remains firmly focused on current lines of enquiry while suspects are on police bail."
Damien had lived with his family in Woodvale Road, Gurnard.
Officers have urged anyone with information to contact them.