Marcia Candian went missing in Lancaster City Centre on Wednesday, November 15.
The 16 year-old has bright pink and purple hair and was last seen wearing a black coat, black leggings and pink training shoes.
A spokesman for the police said: "Can you help us find missing Marcia. She went missing in Lancaster City Centre on Wednesday.
"She may have travelled to Preston and has links to Cambridgeshire where she is originally from.
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"If you know where she is or you can help in any please get in touch."
Anyone with information should contact police on 101.