Michael Pringle, 25, was last seen in the Loch Awe area in the early hours of yesterday.
He and his father had earlier visited the Tight Line pub near Oban and were returning to their campsite when they became separated.
Mr Pringle, from Kilmarnock, Ayrshire, was last seen at around 1am walking on the A85 near Kilchurn Castle.
He is described as around 5ft 9in, slim, with short dark hair and wearing a green camouflage-type jacket over fishing waders.
In 2009 four anglers, who had visited the same pub, went missing after their boat capsized in thick fog.
The anglers had been trying to return to their campsite from the pub which is 500 metres across the loch.
Inspector Julie McLeish, of Oban police office, said: "Michael has never been missing before, and he is not from the area so as time passes we are becoming increasingly concerned for his wellbeing and safety.
"I would like to appeal to anyone who may have seen Michael around the area of Kilchurn Castle to get in touch with police on 01631 510 500."