The woman was running beside the Northern Motorway in St Mary's Bay at about 5am when a man grabbed her.
He dragged her into some bushes near St Mary's Road where he choked and indecently assaulted her.
A passing cyclist heard her screaming and came to her aid. The offender then ran off towards Swift Avenue and Ring Terrace.
He was last seen jumping a fence.
Police said the woman suffered minor injuries and was very shaken by the incident.
The offender was about 180 centimetres tall and of slim build with short black hair.
He was wearing a dark blue jersey with white lettering and is in his mid-20s or younger.
Detective Inspector Scott Beard said it was a random attack by a stranger.
"We want to assure the community that we have a team of investigators working on this case and police will be increasing our frontline presence in the area while we work to identify and catch this offender.
"We are now asking for anyone who saw suspicious activity in the area or for home owners in this vicinity who have CCTV cameras operating to contact the investigation team," said Detective Inspector Beard.
