Natalie Pentland, aged 14, was last seen leaving her home in Brinsworth at around 6pm on Tuesday, June 14.
She has not been seen or heard from since.
South Yorkshire Police said officers and the teenager's family 'are becoming increasingly concerned about her welfare'.
She is white, around 5ft tall, of a medium build and has shoulder length blonde hair and blue eyes.
She was last seen wearing an Army-style tracksuit, jumper and trousers.
Natalie has links to the Chesterfield and Skegness areas.
Anyone with information on her whereabouts should call South Yorkshire Police on 101.