(Image credit: Jeremy Hogan/Bloomington Herald-Times/AP Photo)

Missing Indiana University student Lauren Spierer's parents said today that they do not believe their daughter's disappearance was a "random abduction." They slammed the male friends of their daughter who, they said, were the last to see her before she vanished.

"We have these boys that were there that night that clammed up, shut down, lawyered up," Spierer's father, Robert Spierer, said today on "Katie."

He said it was "very frustrating as the parent of a missing child" to have people who were there the night Spierer disappeared, but have made the sharing of information "impossible or extremely difficult."

Spierer, 21, vanished on June 3, 2011, after a night out with friends in Bloomington, Ind. The Indiana University student is 4 feet 11 inches tall, and weighs less than 100 pounds. She has blond hair and blue eyes.

"I'm frustrated and I'm angry at this point. We've been stonewalled, to some extent, by the last people to see Lauren, and despite their claims of doing whatever they could do, the fact of the matter is they refused to meet with us except for one of the boys," Robert Spierer said.

Most of the men refused to take police polygraph tests and instead took "independent polygraphs."

Eighteen months later, the family is still looking for answers.

Lauren's mother, Charlene Spierer, tearfully recalled that how the last time she saw her daughter was when she went home to surprise her for Mother's Day.

"She's just a great girl, she's very outgoing and friendly and loving…great sense of humor, would do anything for a friend. She just loved life," Charlene Spierer said. "It's painful every single day."

When asked if any new information on Lauren's case has been learned, Charlene Spierer said, "I don't think we've discovered the right information because we still don't have Lauren."

"I truly don't think it was a random abduction," she said. "I think that somebody that Lauren knew was responsible for the events of that evening."

Since Lauren's disappearance, multiple discoveries of remains have been reported. All turned out to be false alarms.

"I know that the likelihood is remote and I understand that, but there is some part of me, because we have not found her, [that] leaves me with the slimmest of hopes," Robert Spierer said. "We simply don't know what happened to our daughter."

Police say the search for Spierer is still an active investigation. The Spierer family has retained its own private investigators to follow up on tips and leads.