Faye Ashby left her home in North Hull Estate yesterday morning to go to school but did not return as normal afterwards.
A Humberside Police spokesman said: "Our officers and Faye's family are trying to contact her but without success, since yesterday evening when she called home.
"We are urging Faye to call us on 101 to let us know where she is and so we can make sure she is OK."
Faye is described as 5ft 2in and slim with very long hair. She is thought to be wearing a white top and black shorts.
If anyone knows where she is or has seen her, they are asked to call police on 101 and quote log 35 of 27 May.