Police say the discovery of a missing man's burnt-out car in bushland has led them to believe he has been murdered.
Michael Pruiti, 31, was last seen in the Forrestfield area on October 23 about noon.
He was believed to be headed towards the Kalamunda area.
His car, a 2000 Mitsubishi Magna, was found recently in bushland in Bartons Mill.
Major Crime Squad detectives are now treating Mr Pruiti's disappearance as a suspected homicide.
Det-Sen. Sgt James Bradley appealed to those people who knew who killed Mr Pruiti to come forward.
He said Mr Pruiti's sisters had been left "distraught and distressed" by the recent news.
He said finding the car was a major development in the case, but would not comment on whether police or a member of the general public had made the discovery.
The Bartons Mill track is often frequented by four-wheel-drive or motocross enthusiasts.
Anyone with information is asked to contact Crime Stoppers on 1800 333 000.