Ian Bramald, 73, has been missing from his home in Buckie, Moray, since Wednesday.
Volunteers are being asked to gather in the car park of the town's Tesco store at 1pm to help with co-ordinated line-searches.
The search area includes fields and anyone attending is asked to dress appropriately.
Mr Bramald is described as between 5ft 10in and 6ft. He has brown hair that is greying and receding on top, and a moustache.
When last seen he was wearing a short, green waterproof jacket, blue corduroy trousers, a cap, a multi-coloured scarf, and glasses.