Police said extra officers are on patrol in the People's Park in Ashington, Northumberland, after the victim was targeted on Wednesday.
Her attacker was in his late 20s, around 5ft 6ins tall, with very short, dark hair. He was wearing a dark tracksuit and blue Nike Air trainers.
Anyone who was in the park around 18:00 BST is urged to call police.
A 16-year-old girl was grabbed from behind and raped as she walked through a park.