The ‘terrifying ordeal’ took place in Bannockburn’s Ladywell Park at 7pm on Saturday, February 10.
The teen was attacked from behind with her attacker dragging her into the wooded area where she was sexually assaulted.
Police have given a description of he suspect who is believed to be male, skinny built and around 5ft 4 inches tall.
He was wearing black clothing, gloves and a hooded top with the hood up and old-looking training shoes. He was well-spoken.
Officers are appealing for anyone with information to come forward.
Detective Chief Inspector Gary Boyd of Stirling Public Protection Unit said: “This has been an absolutely terrifying ordeal for the victim and we are continuing to provide her with all the necessary support and assistance she requires while we progress this investigation.
“I am extremely eager to speak to anyone who has information that can assist us in tracing this suspect.
“This is an area that is popular with groups of young people and I would urge anyone who saw anything suspicious in the area of Ladywell Park to please get in touch.”
Anyone with information is asked to contact officers on 101 or anonymously via Crimestoppers on 0800 555 111 quoting incident number 1065 of 15 February.