Sophie Dearnley, from Huddersfield, was reported missing on December 31 and has links to the Manchester area, West Yorkshire Police said.
A police spokesman said: "She is described as white, around 5ft 4ins tall and of slim build. She wears glasses and has long hair, which was last seen crimped and in a ponytail.
"When she was last seen, Sophie was wearing white lace up trainers, black leggings and a black crop top with Adidas in large white writing across the front.
"She was wearing a dark navy blue waist-length jacket with a brown, furry hood, and was carrying a small, black bag with a black woven strap."
Anyone with information about her whereabouts should call police on 101, quoting log number 1330 of December 31.