Christian Royston, aged 40, from Mexborough, was last seen on Monday, January 4 in the Tennyson Avenue area of Mexborough.
He was last in contact with a family member on January 26, but has not been seen or heard from since, and was reported missing to police on February 15.
Police Constable Amanda Wilson, investigating, said: “Christian has not been in touch with family or friends for three weeks and we are growing increasingly concerned for his welfare.
“I would ask anyone who recognises Christian and has seen him recently or knows where he might be to contact police.”
Christian is described as white, about 5ft 6ins tall with mousey brown hair and of slim build.
Have you seen Christian? Do you know where he might be?
Please call South Yorkshire Police on 101 quoting incident number 790 of 15 Feb