The 19-year-old was on her way home after a night out when a man approached her in Kirkgate at about 5am on Friday.
She told him to leave her alone, but he pushed her against the wall of the Palace pub.
She resisted but he pushed her into bushes on the edge of the Maude Street car park.
Leeds CID said a female passer-by spotted the attack and shouted at the man causing him to run off.
He was described as white, aged 20 to 30 years and of medium build, with fair brown hair.
Detective Sergeant Mark Atkinson of Leeds District CID, said: “This was clearly a terrifying incident for the victim who is being supported by specially trained officers today.
“She received some visible physical injuries and was extremely distressed by what took place.
“It is important we locate this suspect as soon as possible and I would ask anyone who saw a man fitting the description walking alongside the victim near the Palace pub, or the same man fleeing the scene to contact us.”
Anyone with information should call Det Sgt Atkinons at Leeds District CID on 101, quoting log 197 of August 14 or Crimestoppers, anonymously, on 0800 555 111.”