An investigation was launched after police received reports that a man had indecently exposed himself in Chelsea Park, Nether Edge, on Saturday, July 17.
Officers were called at 12.44pm and carried out a search of the area but were unable to locate the culprit.
South Yorkshire Police said: “The suspect is still being sought. The investigation is still ongoing.”
A woman who spotted the man said: “Really concerning as there’s lot of children in this park.
“He was of average height, medium build and had brown hair.”
Two days earlier – at 9.15am on Thursday, July 15 – a dog walkers in Endcliffe Park spotted a a man exposing himself just off a path in a wooded area that leads to Notre Dame High School.
Anyone with information should call 101.