It occurred on Otley Road, near the junction with Cold Bath Road, at around 4pm on 21 November 2017.
The boy was punched in the face which left him with a black eye.
The suspect is aged around 20 with short blond hair on the sides and longer on the top. He was earing a red tartan-patterned jacket ,grey trousers and grey working boots covered in dust.
Officers are appealing for information from drivers of cars or members of the public in the area at the time.
Anyone with information that could assist the investigation should contact the police on 101, select option 2, and ask for Alan Mason . You can also email Alan.Mason@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 12170209401 when providing information.