Madrid, Spain (CNN) -- An American college student has not been seen since early last Saturday after a night out with friends in the Spanish capital. His father, who has since rushed from San Diego, California, to Madrid, is hopeful the police will find him.

San Diego State University student Austin Taylor Bice, 22, arrived in mid-January for a semester of business-course study at a Madrid university, his father, Larry Bice, told CNN late Thursday.

The student went out with five friends last Friday night to a popular Madrid discotheque but was the only one in the group refused entry by doormen, his friends say.

Spanish newspaper El Pais reported doormen kept him out because he was drunk, but a fellow student told CNN it was unclear why he could not get in.

Austin Bice later told an Australian friend waiting outside with him that he would walk home alone and left. That was the last time he was seen by friends.

But photographs of him smiling have started appearing in the Spanish media and on posters that have been attached to walls and street signs near the disco, on the western side of Madrid, and in the city center.

His friends organized the campaign to put up the posters, which read "Missing. Austin Taylor Bice. U.S. citizen, 22, 1.95 meters tall and 100 kilograms" (6 feet, 5 inches and 230 pounds).

He was carrying two credit cards and his California drivers license, said his father, who arrived Wednesday in Madrid and has met three times with the Spanish police and twice with U.S. Consulate officials.

"People we've talked to say if it were bad, it would have shown up right away," Bice said. "It's easier being here than at home. I see what's going on."

The elder Bice declined to be interviewed on camera but talked to a CNN reporter at a cafe near the three-bedroom apartment that his son has shared with a young married couple and another single man.

"I'm really, really worried," said a Spanish student friend, who gave her name only as Tamara. "Because it's not common. He is a very responsible boy. So he cannot just go and not say to any of his friends."

A U.S. Embassy official confirmed the missing-person report and said he could not remember the last time an American student here had gone missing in Spain.

The U.S.-based Institute of International Education said that in 2007, Spain was the third most popular destination worldwide for Americans studying abroad, after the United Kingdom and Italy. It said there were about 17,000 American students in Spain.

Bice was studying in Madrid at the University of Carlos III, which has 18,000 students, of whom 1,500 are from abroad, including about 220 Americans, the school's director of international relations, Carlos Lopez Terradas, told CNN.

The police are reviewing closed-circuit camera footage from Madrid's metro system to see if they can spot Bice, Lopez said.

Friends say they called Madrid hospitals soon after Bice went missing, but to no avail.

His father, an accountant, said, "It's been hard, real hard. These are the things you hope never happen to you."

He added he would remain in Madrid to closely follow the search for his son "as long as I need to."