Kai Challis, aged 16, from Didcot, was last seen on Friday (21/1) evening in Park Road.
Kai is described as 5ft 8ins tall, with light brown hair, and of a slim build. He was last seen wearing black tracksuit bottoms and a black hooded jumper.
He has links to Maidstone and Ashford in Kent.
PC Sam Goodsell, based at Henley police station, said: “We are becoming increasingly concerned for the welfare of Kai and are appealing for the help of the public in finding him.
“I would urge anyone who may have seen Kai, or anyone who thinks they know where he is to please get in touch by calling 101 quoting reference 43220031368.”