Johnstone man James Cassidy, aged 75, has not been seen since 10.30am on Tuesday when he was spotted in High Street, Johnstone, boarding a McGill's bus to Glasgow.
Police Scotland's Inspector Gerry McBride said: "It is completely out of character for James to go missing and his family are extremely concerned as he hasn't been in contact with them.
"He is described as white, 5ft8in in height and of slim build and bald.
"He was wearing a black St Mirren Football Club beanie hat, a black and grey three-quarter length hooded padded jacket, blue jeans and white trainers.
"Each day he gets the bus around the same time to travel into Glasgow city centre, where he goes for coffee then returns home.
"I would urge anyone who recognises his description, or knows of his whereabouts to contact Police Scotland on 101."