Neil Skinner, 71, was last seen camping close to Loch Dochard in the Bridge of Orchy area of Argyll on Sunday May 8.
Police have been searching the area with support from the Air Support Unit, Marine Unit and mountain rescue teams, but have found no trace of him.
Mr Skinner’s family urged anyone who has seen him to come forward.
They said: “As a family we are distraught that our dad has been missing for this length of time and we are desperately seeking answers as to what has happened to him, to help us understand and come to terms with his sudden disappearance.
“If anyone has any information regarding our Dad that they feel may be at all relevant we ask you to please contact police.”
Mr Skinner, from Doncaster in Yorkshire, is described as 5ft 8ins tall with short, white hair, a white goatee-type beard and wearing glasses.
When last seen he was wearing a green jacket and grey walking trousers.
Sergeant Karen MacLennan of Police Scotland said: “Since Neil was reported missing, we have been carrying out searches and inquiries to try to trace him.
“Neil has not made any contact with family or friends since he was reported missing and we are keen to speak to anyone who might have seen him since Sunday May 8, or who has information relevant to our investigation.”
Anyone with information is asked to contact police via 101, quoting reference 3775 of May 9.