Emma Cook, 15, and Melissa Langan, 16, are believed to be in Wakefield.
Emma was described as of slim build and about 5ft 6ins tall. She was last seen wearing blue jeans, a grey and white stripe top and white trainers.
Melissa was last seen wearing a grey hooded jacket, black trainers and black leggings or jeans.
Det Sergeant Phil Davis, of Wakefield police, said: “We believe Emma and Melissa are together and we would urge anyone with any information as to their whereabouts to contact police.”
Anyone with information is asked to contact police on 101, quoting log number 1905 of September 1.