John Parker, aged 54, has not been seen since around 8pm on Saturday, October 28 when he left his home in Warmsworth Road, Balby.
Mr Parker is white, slim, 5ft 4ins tall and has no front teeth.
He has long, grey hair at the sides and an unkempt grey beard.
It is thought he was possibly wearing a blue padded coat and grey pyjama bottoms when he was last seen.
Anyone with information on his whereabouts should call South Yorkshire Police on 101, quoting incident number 57 of October 29.