The girl, 17, was walking along Perth's Scott Street on Monday at 1.20pm when she was attacked. Police said she was shocked but not injured during the incident.
The suspect is described as a man aged between 55 and 60, who is around 5ft 7ins tall with a medium build. At the time of the attack he wore a purple t-shirt and dark denim jeans.
Detectives are reviewing CCTV footage and have appealed for anyone with information to contact them on 0300 111 2222.