Sophie Naylor (16) was last seen in the West Dunbartonshire area at 3pm on Saturday, October 20 on the A82 near to Milton Brae.
She is described as white, 5ft4 and of very slim build.
Sophie has blue eyes and collar-length brown hair which is tied up in a ponytail.
She wears glasses and has piercings above her right eye, her lip and ears and was wearing a dark blue thigh-length jacket with a hood with a faux-fur trim, washed-out denims and white trainers at the time of her disappearance.
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Chief Inspector Damian Armstrong, of Falkirk Police Station, said: “This vulnerable female was previously a resident in the Falkirk area and has a lot of friends and family still living here.
“Police are requesting members of the public who can provide any assistance that would lead to Sophie being traced step forward.”
Police can be contacted on 101, quoting reference number 2506 of Saturday, October 20.