Jayden Fo, who is 16-years-old, has been missing from his home address in Lakeland Drive, Aylesbury since 22 August 2019.
Jayden is described as around 6ft tall and of a large build.
He was last seen wearing a white t-shirt, grey jogging shorts, grey trainers and white socks. He is not believed to have any access to money.
Investigating officer Inspector Darren Deane, based at Aylesbury police station, said: “We are naturally becoming increasingly concerned for Jayden’s welfare, given that he has now been missing for 12 days.
“I am urging anybody who knows of Jayden’s whereabouts, or who believes they have seen him recently, to please contact the 24-hour non-emergency number 101, quoting reference number 43190260262.”