The serious sexual assault happened between 9am and 11am in the playing fields of King James’s School, Knaresborough, when the victim was grabbed by a man.
The victim is a teenage girl from Knaresborough.
She has been receiving support from specially trained officers. The area of the incident has been cordoned off to allow for forensic examination and searches.
Detective Chief Inspector Allan Harder, of North Yorkshire Police, said: “This is an extremely distressing incident and I am appealing for people to come forward if they have any information that may help the investigation.
“I would ask anyone who may have been at King James’s School between 9am and 11am (on Sunday) to contact me as soon as possible. Did you see anyone in the vicinity of the school this morning? Or did you see or hear anything that gave you cause for concern? If so, I need to hear from you.”
Anyone who can help should contact North Yorkshire Police: dial 101, select option 2 and ask for Harrogate CID.
Alternatively, call Crimestoppers anonymously on 0800 555 111. No personal details are taken, information cannot be traced or recorded and you will not go to court.
Quote reference number 176 of 5 April when passing on any information about this incident.