The search for missing Northam man John Irvine continued over Wednesday night with specialist units deployed into the Mundaring State Forest area after his car was found in the vicinity.
As the search begins on Thursday nine mounted police horses, a helicopter specialists trackers and DFES state emergency service volunteers will scour the area.
The 67-year-old was last seen at a roadhouse in Quairading around 2.30pm on Sunday afternoon.
He was driving a brand new blue Toyota Corolla hatchback with licence plate 1GPE156.
A forward command post has been set up at the intersection of Smit and Yarra Road in Flynn within the state forest.
Mr Irvine is described as fair skinned with a slim build, approximately 165cms tall, with white hair, green eyes and speaks with a strong Scottish accent.
Mr Irvine may have been wearing either dark drill pants, a polo shirt and joggers or black tracksuit pants and a blue/black t-shirt.
Anyone who sees Mr Irvine is asked to contact police on 131 444.