Tabitha Zhakata, aged 14, was last seen at 2.30pm on Saturday, January 25 when she left her home in Dinnington to go and meet a friend.
She was reported missing the following day by her sister when she failed to return home.
Tabitha is around 5ft 7in tall, of a medium build and is described as looking older than 14.
She may be wearing black, ripped jeans and a black jacket with a hood.
It is thought that Tabitha may have left South Yorkshire and travelled to Luton.
The teenager has been reported missing before and on that occasion she was found out of the county.
Anyone with information on her whereabouts should call South Yorkshire Police on 101 and quote incident number 13 of January 26.