The teenager was sexually assaulted at a bus stop in Harpurhey yesterday morning.
The incident happened around 7.40 at the bus stop opposite Spice Cabin on Fernclough Road.
A man, who was already sat on a bench within the bus stop, then sexually assaulted her.
She turned to face the man, who ran off up Fernclough Road in the direction of the Shiredale pub.
Officers want to speak to a man in connection with the investigation who is described as white, aged in his mid-40s, around 5ft 6ins tall, of large build, with green-blue eyes.
He is balding with dirty blonde hair and was wearing black tracksuit bottoms and a black zip-up hoody.
Detective Inspector Jen Tattersall of GMP’s City of Manchester Division said: “I want to reassure the public that we are treating this incident extremely seriously.
“The girl is being supported by specialist officers while we follow multiple lines of enquiry to trace the offender.
“The local community will notice an increase in police patrols in the area, and we would encourage anyone with concerns to speak to officers.
“Were you in the area at the time of the offence and recognise the description of the offender? If you have any information that can assist our enquiries, please get in touch immediately.”