Family hopes schoolgirl Bung still alive

The heartbroken parents of a missing Melbourne schoolgirl believe she is still alive and hope a $1 million reward will finally give them answers.

Siriyakorn "Bung" Siriboon, 13, vanished nearly three years ago during a short walk to school in what police fear is an abduction or murder, though there are no clear suspects or major leads.

A $1 million reward announced on Tuesday is aimed at convincing a possible accomplice to finally come forward - or someone who has been told details of the crime but so far kept them secret.

Bung's stepfather Fred Pattison says life has been on hold since the 2011 disappearance, but the family has never given up hope.

"We've believed all along, and have to believe all along, that she's still alive. She's coming home," he said.

"I believe that. We want to believe that. We can't believe anything else."

He said the fact she was taken from a busy street without anyone knowing what happened has taken a huge toll on his family, especially his wife Vanidda.

"Think if it was your family or your daughter," he said.

Bung was last seen on the morning of June 2, 2011 by a neighbour three doors down from her house in Boronia, in the city's outer east.

She was wearing her school uniform and carrying a school bag.

Police say there's no evidence she engineered her own disappearance or that someone at her school, Boronia Heights College, is involved, and her family has all been cleared.

Hundreds of registered sex offenders have been questioned. A handful remain "persons of interest" because their alibis can't be corroborated.

A 24-year-old man who claimed to have accidentally killed Bung in a car crash has been questioned twice but released without charge as parts of his story didn't add up.

Detective Inspector John Potter said the best theory remains an abduction of some kind.

"We've got nothing to say exactly what did happen that day," he said.

"It's baffling."