The attack happened between 5pm and 7pm on Saturday, April 24, near the duck pond off Annat Road.
The suspect is described as white, clean shaven, 6ft, medium build, with short light brown/auburn hair, in his 40s.
He was wearing a plain grey round-neck t-shirt, camel coloured chinos and dark brown loafer-style shoes.
Detective Inspector Paul Riley said: “There were groups of people out and about at the time and I am appealing to anyone who saw anything to get in touch.
"I am also asking anyone who was driving in the area and may have dash-cam footage that could help to contact us.
“If you have information that could assist our investigation then please get in touch via 101, quoting incident 3447 of Saturday, 24 April, 2021, or make a call anonymously to the charity Crimestoppers on 0800 555 111.”