Kyle Cox was last seen at around 1pm on Thursday September 14 in Kendal.
He is described as white, of slim build, with short, light-brown hair. He was last seen wearing a black hooded top, black tracksuit bottoms and black trainers.
A police spokesman said: "We are extremely concerned for his welfare and are urging anyone who has seen him, or knows where he may be, to contact us as soon as possible."
Anybody with information should call 101, quoting log number 1445 of September 14th. Alternatively independent charity Crimestoppers can be reached, anonymously, on 0800 555 111.