The suspect, believed to be aged between 15 and 19 years old, is described as white, between 5ft 9 to 5ft 11 tall, of a medium build, with brown hair. He was wearing a black zipped up jacket with his hood pulled up over his head.
Detective Constable Annabel Gibson said: “It was a sunny day and lots of people were in the park. Someone will have witnessed this incident and we would like anyone with information to please come forward.
“We take incidents of this nature very seriously and I would like to find the person responsible for this terrible, unprovoked attack.”
Anyone with information or who may have witnessed this assault is asked to call police via 101 quoting reference CAD 4378/04May. To remain anonymous callCrimestoppers on 0800 555 111.