By Madison Park and Ray Sanchez, CNN

(CNN) -- For two weeks, investigators have been searching for clues and conducting hundreds of interviews in the search for Mollie Tibbetts. But it's still unclear what happened to the missing University of Iowa student.

Her family and friends are posting flyers and talking to the public and the media about a new reward fund for information on the whereabouts of the 20-year-old.

On Thursday, her family and Crime Stoppers of Central Iowa held a news conference to announce the fund has so far raised $172,000.

"We believe that Mollie is still alive and, if someone has abducted her, we are pleading with you to please release her," said her mother, Laura Calderwood.

The reward was intended to "help facilitate the process of receiving information anonymously that we can use to pay for her or information that would lead to her location," she said.

"It is our greatest hope that if someone has her that they would just release her and claim that money that we have raised for her freedom."

Calderwood said she feels her daughter's presence every day.

"Sometimes I just feel her sitting on my shoulder," she said. "Mollie was an incredibly strong young woman, and I don't know that I have the strength in me but Mollie is lending me her strength every day, every night."

Rob Tibbetts, the young woman's father, called the reward "another tool in our arsenal" to bring her home.

"We're providing this fund to provide some financial incentive for someone who's otherwise reluctant to come forward," he said.

When asked whether he had a message for his missing daughter, the father earlier told HLN, CNN's sister network, "Just hang in there, pie. We're fighting like hell. ... We'll find you."

He also made an appeal should someone be holding his daughter.

"You obviously care for Mollie and, if you're holding her, you've made a huge mistake," he said. "Don't compound it by dragging this out another minute. Let her go and turn yourself in. Face the consequences for the small act that you've done but don't compound it."

Mollie Tibbetts disappeared on July 18 in Brooklyn, Iowa, a small community an hour east of Des Moines, according to the Poweshiek County Sheriff's Office.

More than 200 interviews have been conducted in the investigation into her disappearance, said Richard Rahn, the special agent in charge with the Iowa Division of Criminal Investigation for the Major Crime Unit, earlier this week.

Investigators have been looking at various data, including social media and information from a Fitbit that Tibbetts is known to have used.

"It's intolerable. No one just disappears, no one just vanishes without a trace," her father told HLN.

Tibbetts was studying psychology and wanted to get a doctorate and write books, her father said.

On the day she disappeared, her brother dropped Tibbetts off at her boyfriend's house so she could dog-sit, HLN reported. She was last spotted jogging around 7:30 that evening, wearing gym shorts, a black sports bra and running shoes, the sheriff's office said.

Investigators have constructed a possible timeline in the case.

"The timeline is very important, obviously, to us, but it's also been very important to us to get to know Mollie and understand what's normal for Mollie, what's not normal for Mollie," Kevin Winker, director of investigative operations for the Iowa Department of Public Safety, said Tuesday.

When asked if authorities suspect that Tibbetts was abducted, Winker said, "We don't know where Mollie is at right now. And I am not going to draw any conclusions about the circumstances of her disappearance. Other than it is not consistent with her past."

Calderwood said the recent weeks have felt like torture.

"The first night she went missing, I was distraught," Calderwood told CNN affiliate KCCI in Des Moines. "I knew her phone was dead, but I sent her a text saying, 'I love you. We're looking for you. We will find you no matter what.' "