Annaliese Parkinson-Smith (14) from Colne, was reported missing on Tuesday.
She is white, 5ft 3in tall, with dark, shoulder-length hair. She was wearing a black coat, blue denim jacket, black leggings and black Nike trainers.
Sgt Tim Fryer said: “We are growing increasingly concerned following Annaliese’s disappearance.
“We would urge anyone with information or anyone who has seen her to come forward.”
Anyone with information can contact police on 101 quoting log 1455 of April 19.