Faye Dallinger, 15, has been missing since Thursday, November 7 when she disappeared from home in Clayton Brook.
She is described as white, 5ft 6ins tall, with a slim build and long dark (almost black) hair.
Faye is known to have links to Chorley and Preston.
Officers are concerned about Faye and are asking anyone with any information on her whereabouts to phone 101, quoting log number 04/197126/19.