A Melbourne mum has pleaded with her former neighbours to help piece together the final pieces of the mystery about her teenage daughter's presumed kidnapping and murder over 20 years ago.

Homicide detectives are close to solving the cold case disappearance of Prudence Bird from her home in Melbourne's northern suburb of Glenroy.

But police say they still need the cooperation of a remaining few residents in the area to achieve the final breakthrough.

The 13-year-old schoolgirl, also known as Prue, has been feared slain since at least 2009, when police identified notorious Bega schoolgirl killer Les Camilleri as a key suspect in the case.

On Thursday, with the 20th anniversary of Prue's disappearance having just passed, her tearful mum again begged residents who had lived in Glenroy back then to come forward with information.

'Don't think about me as a grieving mum,' Jenny Bird said, her voice trembling, her hands wrapped around a framed photo of her missing daughter.

'Look at her,' she stressed, pointing at the photo.

'She was 13. An innocent little girl that someone has taken and murdered. For nothing!'

'Please help. Please come forward. Someone's got that vital bit of information that we need.'

Ms Bird's daughter vanished on February 2, 1992, when a family friend who was caring for her that day left the house briefly to pack boxes in the garage.
Police located a burnt-out car that was linked to the case and have interviewed their suspect several times.

Detective Inspector John Potter, head of Victoria's homicide squad, says police have a solid lead on their suspect, but can't proceed with charges without the community's help.

He says police strongly believe residents who lived in the Glenroy area back in 1992 will have information that will solve the case.

'They are people that know, that have been associated with others that may have been involved, or were told things or know things,' he told reporters.

'Now is the time to come forward.'

In October 1997, Camilleri kidnapped schoolgirls Lauren Barry and Nichole Collins in Bega, NSW.

With an accomplice, he drove them across the border into Victoria, where they were repeatedly raped and then killed.

He is serving life without parole for the murders.

Police have also previously examined links between missing Prue and associates tied to Melbourne's 1986 Russell Street bombing, which killed a police officer and injured 21 others.

Mr Potter said on Thursday that the squad could not yet eliminate the possibility that a link existed between the two cases.