Her carers didn't know where she was going or who she was with.  She'd be dropped off at odd hours by a man they didn't know and she'd be wearing new clothes or was drug-affected.

Then, 14-year-old Jess was diagnosed with a sexually transmitted infection. Her carers organised for her to meet a sexual offences and child abuse detective, but Jess refused to speak to them.

Jess, who was abused and neglected by her own family, didn't trust police. Without cooperation, Jess could have been seen as too hard to help.

It's at this tipping point that a new police and Department of Health and Human Services initiative trying to stop the sexual exploitation of the state's most vulnerable young people kicks in.

The pilot program, running in Brimbank, Epping, Diamond Creek, Ballarat and Shepparton, stems from the 2015 Cider House taskforce that targeted almost 30 men in Dandenong suspected of luring youths with drugs, money and alcohol for sex.

More than 50 investigations into the potential sexual exploitation of youths, who were mostly in residential care, were initiated this year as part of the new model.

More than 60 charges have been laid and almost 450 harbouring notices have been given out to potential predators banning them from contacting a child.

In Jess' case, a detective spent months building a rapport with her, but police weren't able to identify the older man she had contact with until one of the residential care staff was able to jot down his number plate.

Jess did not tell police she had been sexual assaulted, but she didn't deny she had contact with the man. This was enough for detectives to take out an intervention order against the him and stop the contact with her.

Soon after, Jess reported a sexual assault at the hands of another man to the detective she had been talking to. The man was charged and later convicted.

Sex offence and child abuse investigator Sam Greenham runs the pilot in Brimbank, which covers suburbs such as Sunshine and St Albans.

At the moment, they have five teenagers aged between 14 and 17, all girls, who are considered to be at the highest risk of being exploited, if they haven't been already.

Sergeant Greenham said one child could have as many as 10 people trying to exploit them at any one time.

The men targeting them, he said, were generally aged between 20 and 30. Some have established contact over Facebook or dating apps, or have been introduced through other young people in care. Some have a lengthy criminal history, including for sexual offending, others have none at all.

"Alcohol, drugs, money – that's the main things in exchange. We've had men up to the age of 70 seen sitting in their cars outside residential care units and kids getting in," Sergeant Greenham said.

Most of the teenagers won't talk to police because they don't think they're being exploited – they see it as normal.

"They see it as receiving some sort of benefit from it," Sergeant Greenham said.

That's why disruption tactics have been the most effective, he said. Police will knock on the door of a suspect, sometimes taking a photo of the child to ask if they know who are they are and what their actual age is.

"A lot of the time we get a lie," Sergeant Greenham said.

"But we give them that warning and hopefully that breaks the connection between them."

If it doesn't, that's when harbouring notices and intervention orders come into play, giving police an evidence trail they can use in court to prove they told an offender how old the young person was.

Such was the case with a Children's Court security guard who was convicted last year of having sex with a 14-year-old girl he met outside court.

He claimed he thought the girl, who was in residential care, was 17, but detectives were able to provide proof they warned him of her age previously.

Assistant Commissioner Dean McWhirter said the long term aim was to reduce a cycle of trauma.

"Young people that have been traumatised, they then move out of care and into young adulthood and into other relationships and does that cycle continue on because that's their learned behaviour?" Mr McWhirter said.

"We need to have some way of actually engaging with them to try and stop the cycle for their children and their relationships, for other children and their relationships."

*Not her real name.