Charlene was 14 when she was last seen in Blackpool town centre on November 1, 2003. Despite a long investigation, including fresh CCTV appeals in recent years, police have never found her.
Detectives still investigating the case believe she was sexually exploited and murdered, while a Â£100,000 reward has been offered for information that leads to the conviction of her killer of killers.
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Now Karen Downes, 53, has written about her decade-and-a-half ordeal in the hope it could help other mums like her.
She said: "When Charlene went missing it was horrendous. I kept on thinking she would turn up, that she was just pushing the boundaries and testing my patience.
"I never for a moment believed I would never see her again, that she had been lured into a gang and groomed for sex.
“Looking back though, the clues were there and I just didn’t see them – now I want other mothers to learn from my tragedy.”
She has previously spoken of her frustration at the police investigation into her daughter's disappearance and has now described how she fought to get the case taken seriously at first.
She added: "The police came but they just dismissed Charlene as a runaway. I can’t help feeling we were side-lined because we are uneducated and working class.
“In the end, I was so despairing of the lack of interest in Charlene that I had my own leaflets printed and I handed them out myself, on the streets of Blackpool, night after night. Sometimes it felt as though I was the only one looking for her.”
Karen's book 'Sold in Secret', which comes out tomorrow, tells the story of the impact of Charlene's disappearance on the family.
Two men were put on trial over the schoolgirl's disappearance, with the jury hearing how it was suspected she had been "chopped up" and put "into the kebabs". However, the trial collapsed and the men were eventually paid compensation for false imprisonment.
Speaking about hearing the allegations in court, Karen said: "It was horrific to listen to. As a mother, it almost broke me."
She added: "I will never stop fighting for the truth.
“I’ve written a book because I don’t want Charlene to be forgotten – ever. She lives on through my campaign, and she will always be in my heart.
“If anything positive can come from this, I would like to help other families. I want other mothers to be aware of the signs of grooming – to spot them and act on them – before it is too late.”
Det Ch Insp Richard McCutcheon, of Lancashire Police, said: “We remain committed to finding Charlene’s killer(s) and her body despite it being almost 15 years since she went missing. A Â£100,000 reward remains on offer for information leading to the conviction of her killer(s) or recovery of her body.
“We will continue to not only focus on her disappearance and murder but also on the wider issue of child sexual exploitation in Blackpool, for which we have now secured a number of successful convictions against men who have abused vulnerable teenage girls.
“I would encourage anyone who knows anything about Charlene’s disappearance and death to come forward and speak to us. Similarly if you have been a victim of abuse, please speak to the police. We will listen to you, support you and bring offenders to justice.”
A 51-year-old man arrested last year on suspicion of the murder of Charlene was released under investigation pending further enquiries. He remains under investigation, police said.