The incident happened at around 4.05pm on Tuesday August 27 on New Hall Road when the victim, who was at the junction Black Brook Drive and the footpath which leads across the A483, became aware of a man on her right who indecently assaulted her and walked on towards Ruabon.
He was seen entering the Gower estate at the roundabout junction.
The victim, in her late teens, was not hurt during the incident.
The offender is described as white, between 30 and 45 years old, about 5'9'' tall, slim to medium build with blue eyes and dark grey spikey hair. The gelled spikes appeared vertical over the top of his head.
He was wearing a white t-shirt and dark blue jeans.
Anyone with information is asked to call North Wales Police on 101.