Dylan Bilby was last seen in the Ammersall Road area of Scawthorpe at approximately 4pm on Saturday, November 25.
A South Yorkshire Police spokesman said: "He has not been seen or heard from since and officers are concerned for his welfare.
"Dylan is described as being around 5ft 9ins tall with brown cropped hair, is clean-shaven and of slim build.
"He was last seen wearing a black baseball cap, black tracksuit top, grey t-shirt, grey tracksuit bottoms and khaki coloured trainers.
"Dylan is known to regularly frequent Doncaster town centre."
Anyone with information on Dylan's whereabouts is asked to call South Yorkshire Police on 101, quoting incident number 1211 of November 25, 2017.