West Yorkshire Police say Monet Williams and Leah Monkman disappeared on Wednesday.
Officers say the teenagers went missing in Leeds and are believed to be together.
They added that Monet was last seen at around 7am wearing black trousers, a black parka with a fur round hood, and a school tie.
She is said to have contacts in the south, east and north areas of Leeds.
The force described Leah as being a white female, 5ft 6ins tall with a heavy-build and brown, shoulder-length hair.
It is understood that she also frequents south, east and north Leeds – as well as Wakefield.
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