A reward of £10,000 is being offered for information about the murder of Scottish schoolgirl Caroline Glachan.
The body of the 14-year-old was found on the banks of the River Leven in Dunbartonshire on 25 August 1996.
Caroline, from Bonhill, was last seen alive going to meet her boyfriend in Renton, after spending the evening with friends.
The schoolgirl’s mother Margaret McKeich, 60, has led appeals, appearing on the BBC’s Crimewatch programme as the inquiry reached 20 years without the killer being found.
Mrs McKeicg said her life had “basically ended” when she was told her daughter had been murdered.
Days before the appeal, she attended a press conference near the site Caroline was last seen alive and called on the community to reveal the killer.
She said: “I would urge anybody to come forward, just to give me that peace and to give me closure.”
Crimestoppers said the reward would be paid for information leading to an arrest and conviction.
Information passed directly to the police will not qualify for the reward.
Angela Parker, national manager for Crimestoppers in Scotland, said: “Twenty years on, and Caroline’s family are still left with unanswered questions as to what happened to her.
“I am asking for people who might have any information, no matter how insignificant they think it might be, to contact Crimestoppers anonymously, because you could be the person that provides the missing pieces to the puzzle.
“We never ask who you are or any of your details. You’ll never speak to anyone from the police or ever go to court. Please do the right thing, and tell us who is responsible for taking a young girl’s life.”
Anyone with information is asked to contact Crimestoppers on 0800 555 111 or through an anonymous online form.
Detectives previously said they were trying to trace a man wearing a hooded top
Last week police said they were following up more than 20 calls after the murder inquiry featured on Crimewatch.
Some calls related to the identity of a hooded man seen near Caroline before she died.
Video contributions to the programme were also made by Mrs McKeich and the schoolgirl’s friend, Joanne Menzies, one of the last people to have seen her alive.
Police Scotland’s Homicide Governance and Review team recently started a fresh investigation and forensic scientists are re-examining more than 300 items collected at the time of Caroline’s death.