A 17-year-old girl was walking through Greenlands Park in Quarry Lane, North Anston, between 9.30pm-9.45pm on Saturday, June 3 when she was approached by an unknown man.
He is reported to have sexually assaulted the girl before leaving the area shortly after.
The man is described as being in his late 20s to early 30s and about 5ft 6in to 5ft 7ins tall.
The girl is receiving support from officers and following numerous enquires in the area, police have now released an e-fit image of a man they would like to trace.
Those with any information about the incident are asked to call 101 quoting incident number 1268 of June 3.
People can also pass information to Crimestoppers anonymously on 0800 555111.