Tips continue to pour in for missing college student Mollie Tibbetts, who disappeared on July 18

Boyfriend Ruled Out as Suspect in Iowa Student's Disappearance — as Police Search Pig Farm

Police in Iowa have ruled out the boyfriend of Mollie Tibbetts as a suspect in the University of Iowa sophomore’s disappearance, which authorities say appears increasingly likely was an abduction.

Authorities tell PEOPLE Dalton Jack has been cooperating with investigators, who have formally excluded him as a suspect.

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Jack addressed his missing girlfriend in a recent interview with the Des Moines Register, saying, “I miss you so much and I love you.”

The search for the missing 20-year-old continues, says Mitch Mortvedt, a spokesman for the Iowa Division of Criminal Investigation.

According to Mortvedt, local, state and federal officers are following up on a number of leads. He confirmed that detectives were searching a pig farm in Guernsey on Thursday morning.

Guernsey is about 15 minutes by car from Brooklyn, Iowa, where Tibbetts was last seen more than a week ago while out for an evening run.

Image zoom Mollie Tibbetts

Mortvedt says that no one has been taken into custody, and noted several searches were being conducted in and around the county.

Speculation that Mollie could not have been abducted by a stranger is misguided, Mortvedt tells PEOPLE.

“One avenue of thought is that if it wasn’t a struggle, and we have found no signs of a struggle, then maybe it was someone she was familiar with,” Mortvedt explains. “But then the other avenue of thought is it could have been a stranger who simply overpowered her or tricked her. We just have very little to go on.”

Mortvedt did confirm to PEOPLE that investigators are interviewing a number of people Tibbetts knows or seems to “have a connection to,” including University of Iowa students and her co-workers.

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Police and volunteers have been looking for any sign of Tibbetts since last Thursday, when her parents reported her missing from Brooklyn, Iowa, where she lives.

The last time she was seen alive was on July 18, when someone spotted her on her regular evening jog in Brooklyn.

She also sent a text message that night at about 7 p.m., and boyfriend Jack opened a Snapchat message from her about 10 p.m., though it’s unclear when she sent it.

The message was a selfie that appeared to have been taken indoors, Jack has reportedly said. He said he last saw Tibbetts on July 16 before traveling some two hours away for a construction job.

Tibbetts is described as 5-foot-3-inches tall, weighing about 120 lbs., with long brown hair and brown eyes.

The rising sophomore at the University of Iowa, described by friends as sweet and sunny, was staying at her boyfriend’s house and dog-sitting for him at the time of her disappearance.

Investigators are also poring over the data recovered from Tibbetts’ social media accounts and her fitness tracker as well as extensive surveillance footage from the area.