The last sighting of Tony Parsons, 63, was at the Bridge of Orchy Hotel in Argyll and Bute at around 11.30pm on Friday 29 September.
He left the area heading south on the A82 towards Tyndrum.
Earlier on that day he had travelled to Fort William by train and was cycling back to Tillicoultry, Clackmannanshire.
Mountain rescue teams and the police dog unit have searched along the route Mr Parsons was likely to have taken but no trace of him has been found.
He is 5ft 9in with a stocky build, short greying hair and a moustache. He usually wears glasses and has a tattoo of an anchor on his right upper arm and a tattoo of an eagle on his left arm.
Mr Parsons was last seen wearing a red waterproof jacket, a blue long-sleeved cycling top, a high-visibility vest, fingerless gloves, beige combat trousers and walking boots.
He was also wearing a silver and grey cycling helmet, carrying a silver and blue rucksack and riding a yellow bike with black handlebars.
Chief Inspector Drew Sinclair said: “Since Tony was reported missing, numerous officers have assisted with the search activity which has been supported by specialist resources, including the dog unit and Killin, Oban, Arrochar and our own Police Scotland Mountain Rescue Teams.
“Motorists and haulage firms which use the A82 and members of the local communities in the Bridge of Orchy and Tyndrum areas have been spoken to as part of our efforts to trace Tony and I want to thank everyone who has so far assisted with our searches and appeals for information.
“Sadly, Tony remains missing and his family have had to go through Christmas without him and without answers as to where he is. Any information, no matter how small it may seem, could be key to helping us find Tony.
“I would continue to appeal for anyone who saw a man matching Tony’s description or who may have seen, found or taken possession of a yellow bike along the route of the A82 on September 29 or in the days after to contact us as soon as possible.”