Andrew Bedford, 27, from Huntingdon, was last seen at 18:20 BST on Friday, 28 September 1990 at Factory Bank, off Great Whyte, Ramsey.
Three people were arrested at the time but no-one was charged.
Specialist equipment is being used to identify disturbances in the earth near Stocking Fen Road in Ramsey.
The investigation into Mr Bedford's disappearance was re-launched as a murder inquiry on Friday.
Police now believe he was shot dead sometime during the evening he was last seen.
Det Sgt Gordon Blair said: "New intelligence has allowed us to pinpoint this area [Stocking Fen Road] as a viable place to search with a view to recovering potential evidence.
"This could include evidence of how Andrew was killed or where his remains are today."
Mr Bedford was last seen eating a takeaway in a light blue Ford Cortina car.
He was wearing overalls, a khaki jumper, jeans and trainers. He was described as 5ft 8in (1.72m), medium build with mousey blond, curly, shoulder-length hair and had a number of tattoos.
The prime suspect for the shooting is now dead, "but others who were involved have never been brought to justice", a police spokesman said.
Officers investigating a cold case murder of a Cambridgeshire man 25 years ago have started digging an area near to where he was last seen alive.