A 21-year-old woman was raped in Horsham Park in the early hours of Saturday morning.
The public have been asked to help find the young man in his early 20s who is suspected to have carried out the attack.
The shocked woman managed to telephone friends afterwards, and police went to her assistance.
Sussex Police say the woman called police at 3.21am to report that she had been raped in Horsham Park.
A few minutes later a police officer found her in Hurst Road. The woman was in the company of two male friends who she had contacted at 2.42am and they had gone to her assistance.
Her attacker is described as white, aged no more than 22-23, 5′ 10″-5′ 11″ tall, of average build with short dark hair and wearing a white T-shirt.
Detective Inspector Dave Wardley-Wilkins of Sussex Police said: “We are examining CCTV in a bid to locate and identify the suspect and in particular, around the Pavilions in the Park. If you saw anyone of his description in the area between 1.30am and 3.30am please emailor call 101 quoting Operation Akela.
If you wish to pass on information anonymously, please call the independent charity Crimestoppers on 0800 555 111.”
Meanwhile, police have arrested a man over the rape of a vulnerable 32-year-old woman in Worthing Road Horsham. They also want to speak to a second man captured on CCTV shown on this page.
The victim was drinking in the Kings Arms pub in Bishopric on July 12 but left at about 9.30pm that evening with two men.
One of the men, who were both white, had Irish accents and said they were brothers, then raped her behind the Sainsbury’s store in Worthing Road, Horsham.
A 47-year-old man from London has been arrested and questioned on suspicion of rape. He was released on bail until October 5.
Officers are still trying to trace a man who was recorded on CCTV in the area who they would like to speak to.
Detective Constable Karrie Bohanna said: “Although we have made an arrest we still need the public’s help to trace the man in the CCTV.
“If you have any idea who he is or where he could be, please contact us.”
Anyone with information should email firstname.lastname@example.org quoting serial 442 of 30/01, call 101 or contact the independent charity Crimestoppers anonymously on 0800 555 111.