Michael O'Grady, 64, vanished after departing Loch Ossian Youth Hostel to walk to Culra Bothy, the starting point for Ben Alder and other Munros on December 22 last year.
Police have released an image of Mr O'Grady, who is from Irvinestown, Co Fermanagh, and believe he may have made it close to Ben Alder, where he is thought to have been spoken by other outdoors enthusiasts.
They also want to speak to anyone who may have seen or spoken to him on December 22.
The bespectacled, experienced walker is described as 5ft 6in, of slim build, with grey hair.
Police Scotland are eager to speak with anyone who may have seen or spoken to him that day and urged them to get in contact.