They are appealing for witnesses to the assault that took place in Croyland Park on Wednesday, April 4.
The young woman was walking in the park between 4.40pm and 4.50pm when she was approached by a teenage boy who pushed her into a fence and sexually assaulted her. The incident took place near the alleyway which leads into Mannock Road.
The offender was a teenage boy aged about 18, white, of slim build and 5ft 5in. He had short blonde hair with a quiff swept to the side. He wore a black Adidas tracksuit with a zip up top and black rimmed glasses.
Officers would like to speak to anyone who may have witnessed this incident or who may have any information regarding it. They would also like anyone who has private CCTV cameras in the area to make contact with them.
Witnesses or anyone with information can contact police on 101 or Crimestoppers anonymously on 0800 555 111, quoting incident number 18000183849