The 18-year-old was attacked at about 2.30am last Sunday in Paisley Road West, Glasgow. She spoke to the man near the Swallow Hotel, then sat on a wall smoking. He forced her into the hotel car park and sexually assaulted her, Strathclyde Police said.
The woman ran away and flagged down a taxi, which took her to a friend's house.
The suspect is described as being in his 40s, of medium build, slightly overweight and wearing a dark leather jacket.
Detective Constable Sandy Ward, of Govan CID, said: "Despite examining CCTV and carrying out extensive inquiries, we have yet to trace any witnesses to this incident. I would like to speak to anyone who may have seen this woman and man sitting on the wall outside the Swallow Hotel.
"I especially would like the taxi driver who picked the woman up and drove her to Middleton Street to contact the police."