A $200,000 reward has been offered for information about the disappearance of Sydney mum Lynette Dawson, last seen 32 years ago on the northern beaches.

The family of a Sydney woman missing for 32 years know she’s been murdered.

They now hope the announcement of a $200,000 reward will uncover the killer of the devoted mother of two daughters, now in their mid 30s, and answer the question of why she was killed.

The family also does not know why Lynette Dawson’s husband Christopher, waited six weeks before he reported his wife missing.

Mr Dawson, who now lives in Queensland, was last questioned about his wife’s disappearance in 1991, and police say he is still a suspect.

Two coronial inquests even found that a “known person” was responsible for her death and forwarded her case to the director of public prosecutions, but to no avail.

“There is no doubt in their minds that Mrs Dawson has been murdered,” Detective Sergeant Damian Loone, who is leading the investigation, said on Thursday.

“But it’s a jigsaw puzzle and we still need information to get a clearer message.”

He and Mrs Dawson’s family hope Thursday’s announcement of a $200,000 reward will finally help them uncover what happened to her.

According to police, Mrs Dawson was last seen on January 9, 1982.

The night before she vanished, the 33-year-old was at home with her husband in Sydney’s northern beaches when she called her mother.

The pair agreed to meet for lunch at Northbridge Baths in Sydney the following day.

But she never arrived.

She was officially reported missing on February 18, 1982 by Mr Dawson.

Police are now appealing to anyone who was a student or a teacher at Mrs Dawson’s old school, Cromer High School, between the 1970s and `80s to contact them.

“For her family, the pain has not diminished,” her brother, Greg Simms, told reporters.

He also had a message for the person responsible for his sister’s disappearance.

“You don’t have any conscience, and you have enabled yourself to carry on your life as a lie.

“If you had any sense of decency, you would come forward and allow us some closure and justice for our sister.”

Anyone with information should contact Crime Stoppers on 1800 333 000.