As many as 70 officers from seven law enforcement agencies walked block by block Friday afternoon in Dinkytown and the surrounding area in search of a University of Minnesota student who was last seen Tuesday night.

David Michael Miller, 20, left Wilkins Hall, a student dormitory in the northwest corner of campus, near Dinkytown, about 9 p.m. Tuesday. Surveillance footage appeared to show him walking west, toward Interstate 35W, said University Police Chief Matthew Clark.

On Thursday, police scoured the Mississippi River by boat, used police dogs and put drones and a State Patrol helicopter in the air to search for the third-year bioscience major from St. Peter, Minn.

But there has been no sign of Miller, who is described as 6 feet 1 inch tall and 175 pounds, with green eyes and brown hair. He was wearing dark pants and a dark jacket at the time he disappeared, authorities said.

Officers from the Minneapolis and St. Paul police departments, the Ramsey and Hennepin County sheriff’s offices, the State Patrol and Metro Transit police set out at 1 p.m. from a command post at 11th and University avenues SE. Officers conducted a “grid search,” meaning each officer had an assigned area “that is thoroughly searched,” Clark said.

Clark said he welcomed the extra help from neighboring law enforcement agencies.

Meanwhile, authorities are conducting second interviews with people who knew Miller and following up on tips phoned into the U’s Police Department at 612-624-2677.

Miller was reported missing after his roommates said he didn’t come home Tuesday night and then didn’t show up for a final exam the next morning, 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 have been unable to track his movements on the campus network of roughly 2,000 surveillance cameras.

As hours pass, “everybody is concerned,” Clark said. “We don’t have a ton of good information. We are hoping for a positive resolution.”