A teenage girl was left "extremely distressed" after being raped in a lane in Glasgow city centre, police said.
The 18-year-old was attacked in Mitchell Lane at about 0300 GMT after becoming separated from her friends.
The attacker was white, of muscular build and had dark hair. He was wearing a long-sleeved top and dark dress-trousers with a square-buckled belt.
Strathclyde Police said they were checking CCTV footage and have appealed for witnesses to get in contact.
The force said the attacker had begun talking with the girl as she looked for her friends, but that as the pair approached Mitchell Lane, he assaulted her.
Det Insp Fil Capaldi said: "This young woman is understandably extremely distressed and upset by her ordeal and it is vital that we find the person responsible."
He added: "The area would have been busy with revellers leaving local nightclubs and I would urge anyone who may have been in the area of Mitchell Lane around the time of the attack to get in touch with us.
"It is possible that people may have seen this couple and have information which could assist our investigation."