James Dobson, from Morecambe, was last seen on November 25 outside the Magistrates' Court in Lawson Street, Preston.
He is believed to have headed in the direction of Preston train station, but was not seen to enter the station.
His whereabouts after this are unknown, but the teenager has links to Morecambe, Lancaster, Preston and Blackpool.
James is described as white, with short brown hair and a slim build.
He was last seen wearing a black parka jacket with a fur hood and a long sleeved, air force blue North Face top.
PC Monk, of Lancaster Police, said: "We are concerned about James and are asking anybody who has seen him, or has any information at all that could help us find him, to get in touch as soon as possible.
"We are asking anybody who has seen him or knows where he may be to get in touch as soon as possible.
"Similarly we would urge James himself, if he sees this appeal, to make contact with us and let us know he is safe."
Anybody with information is asked to get in touch on 101, quoting log number 0914 of 25/11/2019.