Caine O'Brien has not been seen since July 28, according to Merseyside Police.
But police believe he may have been a passenger in a car that was stopped in the Ruabon area on August 1.
The 17-year-old is known to frequent Lancashire – including Skelmersdale – as well as St Helens, Liverpool, Wrexham, Runcorn, Widnes and Warrington.
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He is described as a white male, 5ft 11in tall, of medium build with collar length curly brown hair.
Caine was last seen wearing a blue coat with a hood and blue tracksuit bottoms and carrying a black bag.
Anyone who has seen Caine or knows of his whereabouts is asked to call 101 or direct message @MerPolCC.
Sightings can also be reported online at www.merseyside.police.uk/ro/report/mp/v2/report-sighting-of-missing-person-form/.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.