Breanna-Reshaun Hibbert was last seen at her home in St Helens, Merseyside, on Friday, December 20.
The teenager is known to frequent Manchester, Worsley, Lancashire and St Helens and it is believed that Breanna may be in Bedford or Stroud.
She is described as black, 5ft 7in tall, of slim build, with short black hair and long, red curly extensions. She has brown eyes and wears glasses.
Breanna was last seen wearing a black coat with purple panels on the shoulders, blue jeans and black Timberland boots with white fur around the top. She was also carrying a black holdall.
Anyone with information is asked to contact Merseyside Police Contact Centre, call 101 or pass information on via Missing People on 116 000.