The teenager managed to run away and called police, after the man seized her near the boating pond in Springburn Park, Glasgow.
Officers appealed for information about the incident, which happened at about 9pm on Saturday.
Detective Sergeant Larry Dempsey at Maryhill CID said: “This was a very frightening experience for the young teenage girl and luckily she managed to run away from the suspect.
“It is vital that we trace the man responsible and we are currently reviewing any available CCTV in the area.”
He urged anyone who was in the park on Saturday evening and saw a man dressed in dark clothing hanging around there to contact police immediately.
Anyone with information is asked to contact officers at Maryhill via telephone number 101 quoting incident number 4445 of April 17 or Crimestoppers on 0800 555 111 where anonymity can be maintained.