Leon Bulmer, aged 16, from Scunthorpe, but who has links to Sheffield, was reported missing by his mother at the end of November.
He is white, around 5ft 11ins tall, slim and has short, light brown hair and brown eyes.
When last seen he was wearing black jeans, a black top and a blue body warmer.
Police officers believe he is safe but want to see him face-to-face to confirm.
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A Humberside Police spokesman said: "We believe Leon is safe but until we can see him face to face we cannot be sure that he is not in any harm.
"Leon, if you see this message, please ring us on 101 and talk to us, we only want to make sure you are ok."
He added: "We're concerned about him due to his age and are urging anyone with information about Leon or where he is now to call us."