Police say they are increasingly concerned for the welfare of 15-year-old Marcus Thomas, who hasn't been since since Wednesday 14 June.
He is described as 5ft 7in tall, of slim build, with brown shoulder-length hair extensions, blue eyes and a Welsh accent.
He is also known as Nicola Joe Thomas and was last seen wearing white jeans, black canvas pumps, a Minnie Mouse t-shirt, a grey marl cardigan and carrying a black and pink bag. He may also be wearing make-up and hoop earrings.
Police say he could be in Greater Manchester, Lancashire, Cardiff or Caerphilly.
Sergeant Jim Arkwright of Greater Manchester Police said: “No-one has heard from Marcus for more than 48 hours now and our concerns are increasingly growing".
Anyone with more information is asked to contact police on 101 quoting reference MP/17/0107300.