North Yorkshire Police is appealing for information after the offence occurred at around 9.15pm on Tuesday, March 28, as the victim was walking on West Street.
Officers want to identify a white man, around 5ft 9ins in height, of slim build, with short dark hair.
He was wearing dark clothing and dark trainers and was seen in the area around the time of the offence.
He is thought to have approached the victim from behind from the direction of Avenue Victoria and returned in this direction following the incident.
Anyone with information is asked to call101, select option two, and askfor PC Leah Gillon (596). Information can also be provided by email on [email protected]
Quote reference 12170052442.