The 14-year-old victim was walking through Hexthorpe Park near to the gates for the bike rack when a man approached her and asked for the time.
READ MORE: Hunt for sex predator who attacked schoolgirl in Doncaster parkPolice said he then grabbed the girl and subjected her to a terrifying sexual assault before making off in the direction of Oswin Avenue.
Officers have now released e-fit pictures fitting the description, which have been produced by the victim and a witness.
It also emerged that the man had followed another woman around the time of the attack on Wednesday, April 11, at 3.20pm.
“This investigation is an absolute priority for us and since Wednesday we’ve conducted numerous house to house enquiries, spoken to potential witnesses and increased our patrols in the area.
“Since the incident was reported to us, a number of people have reported seeing the man walking in the area.
“This includes a woman who was walking her dog through the park at around 12pm on Saturday, April 14. The man is said to have followed her closely as she walked through the park before he left towards the bandstand when a family approached.
"The man never spoke to the woman or came in to physical contact with her but we do believe it to be the same man who assaulted the girl last week. He is described as being 18-20-years-old and is said to have been wearing black shoes, blue jeans and a red coat."
The victim has been supported by specialist officers following the ordeal.
Meanwhile, police have also stepped up patrols in the area.
“If know who the man is, or think you’ve seen him in the area, please don’t hesitate to contact us. You can pass information to 101 or call Crimestoppers anonymously on 0800 555111.
"Please quote incident number 618 of 11 April when passing on information."