Detectives say the teenager was attacked between Regent Street and Shepherd Road on Tuesday, April 25 between 5.30pm and 6pm.
It is understood that an unknown man approached the teenage girl and subjected her to a serious sexual assault before leaving the scene.
Officers are releasing a description of a man they would like to speak to in connection with the investigation.
He is described as being white, around 6ft tall and around 30-years-old, with a dark beard and of skinny build.
He was is said to have been wearing a dark hooded top, a green t-shirt with a crew neck underneath and a dark woolly hat.
Detective Sergeant Debra Renwick, whose team is investigating the incident, said: “We continue with our enquiries to establish the circumstances surrounding this report and this work will be ongoing over the bank holiday weekend.
“We are working closely with the victim providing support and there will be increased, high visibility patrols in the local community to provide further reassurance.
“I’d ask anyone that may have been in that area on Tuesday evening, who may have witnessed suspicious activity, to get in touch with police.”
Any information call 101 or email [email protected] quoting incident number 971 of April 25.
You can also ring Crimestoppers anonymously on 0800 555 111.