Kye Albelda, also known as Kye Bowry, went missing from Lincoln on Wednesday, October 11 and officers investigating the disappearance believed he may have travelled to Doncaster or London.
Kye is 6ft tall, slim and has plaited hair. When he was last seen he was wearing blue Nike tracksuit bottoms and a sweatshirt.
A Lincolnshire Police spokesman said: "We are appealing to Kye to make contact and let someone know he is safe and well."
Anyone who has seen him or believes they know where he is should call Lincolnshire Police on 101 and quote incident number 260 of October 11.