Alistair Lovie was last seen at about 11am on Sunday walking close to disused mines north of Inverarish on the Isle of Raasay.
Searches have involved Police Scotland, HM Coastguard helicopter and ground resources, the Search and Rescue Dogs Association, Skye Mountain Rescue Team, RAF Mountain Rescue Team, the Scottish Fire and Rescue Service and the RNLI.
Local volunteers are also helping with the search for the 72-year-old.
He is described as 5ft 10in, of medium build with brown hair and blue eyes.
When last seen he was wearing a black jacket, jeans, a black cap, a blue shirt and a red jumper.
Inspector Bruce Crawford said: “Sadly, despite extensive searches over the last three days, the last confirmed sighting of Alistair remains on Sunday morning.
“Raasay is a small community and we know that there is considerable concern for Alistair among local residents.
“We would like to thank them for their assistance and support of the agencies taking part in the searches.
“I would ask that people remain vigilant and report anything which may be of use to police as soon as you can.
“If you have a shed or somewhere someone could have sought shelter then please continue to thoroughly check these.”
Anyone with any information is asked to get in touch quoting incident number 2548 of Sunday, March 31 or speak with any police officer.