It's a mystery that has lingered over a small Queensland town for almost a quarter of a century. 

Booyal, in the state's Wide Bay Burnett region, has a population of around 275 and is the kind of place where everyone knows everyone.

And yet in this small country community, the 1999 mysterious disappearance of mother-of-two Christine Fenner, remains unsolved.

For the first time, police are treating the 48-year-old's disappearance as suspected murder and hope a $500,000 reward will help solve the case.

Speaking on Thursday, Ms Fenner's son Norton Turner said the unexplained loss of his mother had left his family in limbo.

"I still have dreams about Mum, and I wake up crying," Mr Turner said.

"Over the years, the impact that this has had on our lives is more far-reaching than I ever could have imagined.

"I ask anyone out there: How much would you want to know what happened to a member of your family if you were in our position?"

The facts...

At the time of Ms Fenner's disappearance in February 1999, all of her belongings remained in the caravan she shared with her de facto partner Mark Graham at Booyal. Mr Graham has since died.

None of her favourite items including her shoes, glasses, and cigarettes had been touched. Nor had her bank account.

In 2008, coroner Jennifer Batts ruled Ms Fenner — also known as Christine Maria Newman — was dead, but she could not rule on the cause or circumstances of her death.

In her findings, Ms Batts said there was "evidence of a significant argument" between Ms Fenner and Mr Graham the night before she disappeared, but that the relationship was known to generally be a "good" and "happy" one.

The coroner noted that when Ms Fenner disappeared, she was in "extremely poor health" and was known to indulge in "heavy drinking".

There was also no evidence to implicate anyone else in Ms Fenner's death.

The inquest heard that, over the years, police had received tip-offs on four occasions claiming the woman had been murdered.

However, despite searches carried out at different properties across the region, nothing has ever been found.

'Loyalties change'

Over the years there has been speculation as to what happened to Ms Fenner. Had she met with foul play, wandered off, or died of natural causes?

Detective Senior Sergeant Tara Kentwell said police were now appealing for information regarding Ms Fenner's suspected murder.

"There is a $500,000 reward being offered for the information that leads to the apprehension and conviction of the person or persons responsible for the suspected murder of Christine Fenner," she said. 

She said it was "never too late" to come forward with information.

"Relationships and loyalties change … people who were once scared to speak, we encourage them to come forward," Detective Senior Sergeant Kentwell said.

"An appropriate indemnity from prosecution will be recommended for any accomplice who first comes forward with this information.

"We're keeping an open mind and continuing investigations and hopefully we can find some resolution for the family and community."