Scores of volunteers on Tuesday joined the search for a missing University of North Dakota (search) coed who may have been kidnapped, police said.

About 1,300 searchers combed the ground, some of it snow-covered, for rubbish, clothes and other items in hopes of handing Grand Forks police a clue into what happened to 22-year-old Dru Sjodin (search).

Police believe Sjodin may have been abducted Saturday. They said Tuesday that they were working on the assumption she was still alive.

"We have nothing to indicate otherwise," Sgt. Michael Hedlund said.

Police said searchers turned up a number of discarded items, ranging from clothing to paper towels, in ditches and fields southeast of Grand Forks (search), near Fisher, Minn., where a call had been traced to Sjodin's cell phone Saturday night. Grand Forks and Fisher are about a dozen miles apart.

The response to the search for the missing woman was so overwhelming police asked some to stay home late in the day.

Police said "items of interest" were found but did not elaborate. Hedlund said they did not appear to be significant to the case.

"There are things that we are looking into, but to the best of my knowledge, it was nothing they could pinpoint to being in Dru's possession," Hedlund said.

The searchers were bused to the Fisher area, where the wind made the temperature feel like 10 below zero and the ground was covered with snow.

Hannah Schlag, a University of North Dakota student from Velva, was in a group of 12 walking through one five-mile section covered with snow.

"My ankles are getting a little numb, going through the deep stuff," she said. "But I feel this is what I should be doing right now. Biology doesn't seem that important."

A small group of volunteers held hands in a circle and prayed. One called out, "Let's go find Dru," as the group broke up to join the search.

"I was up all night, because I've just been itching to get out and do this," said Jerrod Arneson, one of the searchers. "You never think something like this would happen here, and when it does, you want to do something."

Michelle Vogt said she lived on the same dormitory floor as Sjodin when the two were freshmen.

"She is an awesome person, very fun and outgoing," Vogt said. "I don't know why you wouldn't want to come out and help. I think it's great the way everyone is coming together."

Tim Gerlach, a graduate student, said the search was a priority.

Sjodin's father, Allan, and Hedlund appeared on television morning programs to show Dru Sjodin's picture and ask for help.

"We need a lot of prayer and a lot of hope. We have had a tremendous outpouring of help here. We just want her back," Allan Sjodin said.

The search was to resume Wednesday, but only with law enforcement personnel, Hedlund said. Authorities also are awaiting results from the state crime lab, which is analyzing Sjodin's car.

Sjodin, a graphic arts major from Pequot Lakes, Minn., was last seen late Saturday afternoon, as she was leaving the Columbia Mall store in Grand Forks where she worked. Her mother, Linda Walker, said her daughter was talking to her boyfriend in Minneapolis on her cell phone about 5 p.m. Saturday when he heard her say, "Oh, my God," before the phone went dead.

The boyfriend, whom authorities would not identify, called Sjodin's roommate to ask about her after a second call about three hours later that lasted only about a minute, with no conversation. The roommate called police after Sjodin, who had a reputation for reliability, did not show up for her 9 p.m. shift as a waitress in a Grand Forks bar.

Lt. Dennis Eggebraaten said he did not know why Sjodin's boyfriend did not call police.

"I'm not going to guess what was going on in his mind at the time," Eggebraaten said.

Police traced the second call from Sjodin's cell phone to the area near Fisher. Police said the cell phone signal put it within about five miles of the tower near Fisher from about 8 p.m. Saturday until the signal faded out 24 hours later.

Police said Sjodin's red car was found in a Columbia Mall parking lot with a package inside that she apparently had bought at the mall. They found no sign of a struggle.

Sjodin's family is offering a $20,000 reward. David Sutfin, Sjodin's uncle, told the Grand Forks Herald that an unnamed "private benefactor" had added $20,000.

Sjodin is described as about 5-foot-5, weighing 130 pounds, with frosted blond hair and blue eyes. She was last seen wearing black slacks, black loafers, a pink and purple V-neck blouse, a black blazer-style jacket and a small black handbag.

The Associated Press contributed to this report.