Authorities on Thursday appealed to the public for help in finding a University of Minnesota student who was last seen Tuesday night leaving a dormitory on the school's Minneapolis campus.

Police officers from three law enforcement agencies scoured the Mississippi River by boat, and drones and a State Patrol helicopter searched from the sky for any sign of 20-year-old David Michael Miller, authorities said.

Police say that Miller, a third-year bioscience major from St. Peter, Minn., was last seen walking out of Wilkins Hall, a student dormitory in the northwest corner of campus, near Dinkytown, about 9 p.m. on Tuesday.

Surveillance footage appeared to show him walking west, in the direction of Interstate 35W, said U Police Chief Matthew Clark.

Miller hasn't been "seen or heard from since," authorities said.

Miller, who is described as 6 feet 1 and 175 pounds with green eyes and brown hair, was wearing dark pants and a dark jacket at the time, authorities said.

Miller's roommates, concerned that he never came home that night and then didn't show up for a final exam the following morning, reported his disappearance to campus authorities, Clark said.

Before his disappearance, Miller's roommates reportedly didn't notice anything amiss.

"That's the unusual thing: They didn't say anything about him having emotional issues," Clark said.

Miller left behind his phone, Clark said, complicating the task of finding him. And so far, he said, U police haven't been able to track his movements on the campus network of approximately 2,000 surveillance cameras.

If he isn't found by Friday morning, Clark said, between 40 and 50 officers will start conducting "grid searches" through Dinkytown and surrounding areas.

Authorities urged anyone with information about his whereabouts to contact the U police department at 612-624-2677 or call 911.