The model and dancer's half sister Suellen Simpson said she was hopeful of answers "so that I may finally put her to rest".

"For many years, our family worked tirelessly to find out what happened to my sister - but sadly both our mother and Revelle's father, Ivor, passed away without ever knowing what happened to their little girl," Ms Simpson said.

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"Losing someone that is close to you - you're never the same person again. I truly hope this reward will prompt someone to come forward with information that will help police find those responsible for Revelle's disappearance."

Just 22 when she went missing, Revelle was last seen more than 26 years ago in Sydney's Kingsford area on November 5.

Her mother Jan, a Soldiers Point ballet teacher, was waiting on the platform in Newcastle but her daughter never arrived.

Police later found items including a make-up bag, keys and a shoe scattered in Ainslie Street.

A 1999 coronial inquest found Ms Revelle died at the hands of a person or persons unknown.

It was referred to the Unsolved Homicide Unit, and a formal review last year led to a senior detective from the Centrla Metropolitan Region starting a re-investigation.

That investigation, Strike Force Aramac, on Friday renewed its calls for members of the public to come forward with any information that could help.

Minister for Police and Emergency Services David Elliott announced the reward change on Friday, up from the $250,000 that had been on offer for information to solve the case.

"Ms Balmain was only 22 years old, and her sudden disappearance has been deeply felt by her family and friends for more than 26 years," Minister Elliott said.

"I am optimistic that the significant increase in the reward will help detectives obtain new information relating to Ms Balmain's disappearance and hopefully hold someone to account."

Strike Force Aramac lead investigator Detective Chief Inspector Stuart Bell said new forensic technology had been used on the case in the past six months.

"It is our hope that today's reward will encourage those in the community - including Revelle's friends and co-workers at the time - to come forward and speak with police, so we can hold those involved in her disappearance accountable," he said.

State Crime Command director Detective Chief Superintendent Darren Bennett, said the re-investigation into had significant investigative experience to draw on.

"Over the years, the support from the community in the pursuit to locate Revelle Balmain and piece together her last movements has been very beneficial to police," he said.

"With fresh eyes now being cast over more than two decade's worth of statements and intelligence reports, as well as physical and forensic evidence, it is our hope that justice will be found."

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