It happened at the Pine Woods near Crag Lane, behind Harlow Carr Gardens, at about 4pm on Sunday, 7 October 2018.
The man police are searching for is white, around 6ft tall and slim. He was wearing a blue hat and footwear.
Anyone who saw a man matching his description in the area at the time, or has other information that could assist the investigation, should contact North Yorkshire Police on 101, select option 2, and ask for Brendon Firth. You can also email Brendon.Frith@northyorkshire.pnn.police.uk
If you wish to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote the North Yorkshire Police reference number 1218018756