Mark, who is aged 39, was last seen on Friday, March 4 when he left his relative’s house in the Intake area of Doncaster shortly after 7am.
He was later sighted outside the One Stop store on Sandford Road in Balby on Monday. March 7, but has not been since then.
Mark, who lives in the Conisborough area, is described as white, 5ft 5ins tall, of a medium build and with very short brown hair and a beard.
Officers are becoming increasingly concerned for Mark’s welfare and want to speak to anybody who has seen him.
A police spokesman said: “Have you seen him? Do you know where he might be?”
Anyone who may have any information which may help South Yorkshire Police with their enquiries, please call on 101 quoting the incident number 398 of 8 March.