The 15-year-old suffered an injury to her face in the incident, which happened on a private street to the rear of Swarcliffe Road in the Starbeck area of the town at about 9am yesterday.
Her attacker is said to have been aged between 30 and 40 and around 5ft 9in tall, with scruffy blond hair.
He was wearing a black jacket, grey tracksuit bottoms and blue trainers.
A spokesman for North Yorkshire Police said: “We are requesting the public’s assistance to help establish the full circumstances surrounding the incident.”
Anyone with information is asked to ring the North Yorkshire force on 101 or Crimestoppers anonymously on 0800 555111.