Karen, who is 24 years old and from Cork in Ireland, was last seen walking away from a nightclub in Glasgow's west end after talking to a man outside.
She had been at Sanctuary nightclub on Dumbarton Road from about 23.45 on Saturday night.
At 01:00 she told friends she was going to the toilet but did not return or take her jacket.
She was then seen on CCTV talking to a man outside the club, before leaving and walking towards Church Street.
Miss Buckley is described as white, about 5ft to 5ft 2in (155-160cm) tall, with brown eyes and dark hair with long black curly hair extensions in.
She was said to be wearing an all-in-one black jump suit with red high heels and a black handbag when she disappeared. She speaks in an Irish accent.
A man who was seen with missing student Karen Buckley has been traced and is helping police with inquiries.