The indecent sexual exposure happened in the town’s Valley Gardens on Tuesday, June 7, around 9:15pm.
Officers leading the case have appealed to the public to come forward with any information.
They have conducted door to door inquiries.
A Police Scotland spokesperson said: “Inquiries are ongoing and police are appealing for anyone who was in the area either on foot or in a vehicle and with relevant information or dashcam footage, or CCTV footage, to come forward.
Contact Police Scotland on 101, quoting incident number 3798 of Tuesday June 7.