Friends said Austin Bice, 22, was last seen outside the Riviera concert venue and discotheque in the early morning hours of Feb. 26. The family he was staying with raised the alarm when they realized he was not in his bedroom.
Friend Maria Garcia said Bice and his friends had been drinking at an apartment before going out to the club. A doorman suggested he rest a while before going in because he looked unwell. A friend stayed outside with him until Bice said he was going home.
Larry Bice, the student's father, from Carlsbad, Calif., said he had flown to Madrid to help search for his son and that "the police are doing a great job, they have been very active."
Bice's father said his son was physically fit, tall - six-foot-four - and had recently climbed Mt. Whitney with his father.
Garcia said Bice had only been in Madrid for a month and a half, so was not yet fully acquainted with the area. She said that police and later friends had carefully combed the area around the club and found no trace of Bice.
The Associated Press contributed to this report.