Mr Price-Purcell was last seen getting into a bright yellow Holden Commodore sedan in north Brisbane on February 16, 2015.

Three years on, his mother Leoni Price is appealing for information.

Ms Price says the loss of her 25-year-old son is something the family continues struggling to come to terms with.

"Our whole family grieve for him every day," Ms Price told reporters.

"He's in our hearts and our thoughts every day, and we need to know what happened so that we can have some peace."

Police believe Mr Price-Purcell, better known as Sam Price, was driven in the Commodore to the Toowoomba area where they say he was murdered.

Ms Price says she now accepts her "stunning, funny, quirky, sporty, amazing" son isn't coming home.

"People tell me it gets easier with time, but it doesn't," she said.

"It changes with time and the realisation slowly comes that we'll never see him again.

"That's a milestone, but it's an incredibly difficult thing to have to come to terms with. The emptiness that I feel, his loss has just left a massive hole in our hearts."

Police are seeking information on the movements of the yellow Commodore around the time of Mr Price-Purcell's disappearance.

They have also issued an appeal to locate a 2000 Subaru WRX sedan, originally white in colour, but since believed to have been painted pale or sky blue with a large black spoiler.

The vehicle was seen in the Toowoomba area in September 2015.

Detective Inspector Damien Hansen says those involved in Mr Price-Purcell's death have a limited opportunity to come forward and assist police, with a group of people of interest on their radar.

"Some of those people are no longer mixing in those circles, they've moved on with their lives, they've started families," Det Insp Hansen told reporters.

"This will not go away. I would encourage those people to come forward."

Australian Associated Press