Ian Bramald, 73, left his home in Buckie, Aberdeenshire, at around 9am last Wednesday. He was spotted in an area near Drybridge and Thornybank around half-an-hour later but has not been seen since.
Police and RAF helicopters, coastguard, search dogs and around 80 members of the public have been involved in the search for Mr Bramald but no trace of him has been found.
Officers said they have been "overwhelmed" with the public support for the search, but remain "deeply concerned" for his safety.
Police have released new images showing Mr Bramald wearing glasses, a grey jacket, brown cord trousers and a tartan bunnet, all of which he was wearing when he was last seen.
He is around 5ft 10in in height, with dark receding hair and a grey moustache.
Inspector Colin Mowat said: "We are still deeply concerned to trace Mr Bramald and as time goes on we are growing increasingly anxious.
"Significant resources have been deployed to this inquiry including the Police Scotland helicopter and RAF Lossiemouth's search and rescue helicopter. HM Coastguard volunteers, specialist search dogs and RAF Mountain Rescue have also been involved.
"We have also been absolutely overwhelmed with the support from the public. Around 80 people have volunteered their time and been involved in searches on three occasions now and we would like to thank them for their continued support.
"We would now like to ask people to look at the new photographs issued, giving particular consideration to his clothing."
Anyone with information can contact police on the non-emergency 101 number.