Douglas Macgregor, 64, was last seen leaving his home address in Castletown around midday on Wednesday.
He is described as 5 foot 6 inches tall, with grey/white hair that is receding and thinning.
He is believed to be driving his silver Honda Civic, with registration number: OW56 EVC.
Police believe he is in Shetland.
Constable Stephen Todd from Thurso Police Station said: “We are concerned about Douglas’ wellbeing as he has not been seen or heard from since Wednesday 30th June 2021.
“We are appealing for anyone who recognises Douglas, or has information regarding his whereabouts to please come forward.
“We would also urge Douglas to please get in touch with someone to confirm that he is ok.
“Anyone with information is asked to contact Police Scotland through 101, quoting incident number 1857 of Saturday, 3rd July, 2021.”