The 16-year-old was targeted on Pheonix Golf Course, Brinsworth, at around 9pm on Saturday, December 29.
South Yorkshire Police said she was approached from behind by an 'unknown man' and sexually assaulted.
The attacker was wearing dark blue ripped jeans, a light blue denim jacket and brown, smart shoes.
PC Richard Stump said: 'A thorough investigation is underway and at this stage we are treating this as an isolated incident.
'We are working with the victim and her family to offer them support and reassurance.
'It is incredibly important that anyone who has any information contacts us.'
Call South Yorkshire Police on 101 and quoteÂ crime reference number 14/189036/18.