Updated

Purdue University police plan to search rural areas and the Wabash River banks Saturday for clues about the disappearance of 19-year-old Wade Steffey, while they also look for a second Purdue student who is missing.

The West Lafayette Police Department, the FBI, the Purdue University Police Department, and the Tippecanoe County Sheriff's Department all are helping search for Steffey, a native of Bloomington, Ind.

Investigators used K9 units to search campus properties, while the Tippecanoe County Sheriff's Department has used boats to search the nearby Wabash River. The FBI has used sonar technology to search nearby ponds.

Previous sweeps by volunteers, police, search dogs and a helicopter have turned up no signs of Steffey. He was last seen after a party at the Phi Kappa Theta fraternity house on the north side of campus early Jan. 13.

He was reported missing after friends returned from the school's three-day break for the Martin Luther King Jr. holiday and could not find him.

Police are looking for volunteers to help search. Drivers who have all-terrain vehicles or horses will be asked to focus on rural areas, while some of the volunteers on foot will be sent to the banks of the Wabash, said Purdue spokeswoman Jeanne Norberg.

Police also are asking property owners to volunteer to have their private lands searched, she said in a news release.

University spokeswoman Norberg said more than 300 people have already volunteered. More than 1,000 volunteers have taken part in searches of the campus and surrounding areas, and police have tracked hundreds of tips.

"We welcome anyone else who can help. Obviously, anyone with access to an ATV or horse is urged to volunteer," Norberg told The Journal and Courier, adding Those who can't search can help by providing gasoline cards to help defray ATV expenses, she added.

Volunteers are asked to call the Wade Steffey Volunteer Center at (765) 496-2289 to provide their contact information so they can be alerted of plans for such mass searches.

Meanwhile, Purdue police are also involved in another search for a second missing student, but investigators do not believe the two cases are connected.

Doctoral student Eric M. Campbell of Avilla disappeared during a trip to Texas and Mexico.

“The timelines are different,” Norberg said in a statement. “Wade was last seen shortly after midnight Jan. 13. Campbell was in El Paso on Jan. 12 and then arrived in Mexico at 8 p.m. that day.”

Campbell’s luggage arrived at Indianapolis International Airport after he bought a ticket to fly back to Indiana from El Paso on Jan. 18, investigators said.

Norberg said there is no evidence the 33-year-old student ever boarded the flight.

“It is puzzling that he didn’t come back,” she said.

Campbell left campus Jan. 8 to travel to El Paso en route to a wedding in Juarez, Mexico.

Purdue police contacted police in El Paso 10 days later after he did not return.

According to the Purdue University's Journal and Courier, Karen Campbell said her son regularly traveled to the El Paso area, where his girlfriend lived. But she said there was no reason to suspect he might stay.

"He was excited to be back at school," Karen Campbell told the newspaper. "We saw him on the seventh and helped him get stuff for his room."

A friend of Campbell’s who lives in Mexico told police he had returned to the United States on Jan. 15, and police confirmed he bought an airline ticket to Indianapolis in El Paso on Jan. 18 but never arrived. Campbell’s mother told police that she has not heard from him, Norberg said.

"We always hear from him at least once a month and get an e-mail at least once a week, even if it's just a short note," Karen Campbell told the Journal and Courier. "So this has just been way too long."

The last anyone heard from him was when he called a friend who was supposed to take him back to the airport for his return flight. Campbell told his friend that he had another ride.

A missing person's report was filed by the parents on Friday. Norberg said the university did not know the report was filed until Tuesday.

Campbell, who had worked as an engineer in Mexico after receiving a master’s degree from Purdue in 2000, had recently enrolled as a doctoral student at the West Lafayette campus.

Karen Campbell said her son was always cheerful and joking around.

"In some ways, I keep expecting him to call laughing at me for ever worrying," she said.

The Associated Press contributed to this report.