Mom of missing Iowa student Mollie Tibbetts says giving up hope is 'not an option'

Laura Calderwood's 20-year-old daughter Mollie Tibbetts has been missing for more than a week. Though investigators are calling the case unusual, she's not giving up hope.

"There's really no clues," Calderwood told Good Morning America in an exclusive interview on Friday. "There's a DCI agent who said she's been in the business for 23 years and only one other case where she had so few leads. So I really can't speculate. I'm just hoping for the best."

Investigators are expected to announce an update on Friday. The Brooklyn, Iowa resident was last seen on Wednesday, July 18, when her older brother Jake dropped her off at her boyfriends' house, where she was living for the summer. Tibbetts was alone with the dogs while her boyfriend, Jack Dalton, worked at his construction job about 100 miles away. Investigators have already announced that Jack and both of Tibbetts' brothers were cleared as suspects.

Based on a timeline constructed by investigators, Tibbetts left for a run a couple hours after her brother dropped her off. Her activities after that are unclear.

Her loved ones found out something was wrong the next day.

"My son, Scott, he gave me a call about 5:15 p.m. saying, 'Mom, did you know Mollie didn't go to work?' At which point I said, 'I will be right home," Calderwood said.

Since then, hundreds have joined in the search, which is now being conducted with the help of the FBI and the Iowa Division of Criminal Investigation. Investigators said they have not ruled out abduction.

As the days stretch on, Calderwood said she can't give up hope that her daughter will be home soon. She hopes she can be found in time to travel to Jack's brother's wedding next week.

"She was very much looking forward to this vacation she and Dalton were going to take to the Dominican Republic," she said. "First part of August. She had her first passport."

Earlier in the week, Calderwood had spoken to ABC News about her daughter's personality and her plans for the future. She was set to start her sophomore year at the University of Iowa.

"She is just such an outgoing, fun, loving life, loving person," she said. "She was getting ready to move into her first apartment."

Tibbetts' brother Scott said earlier in the week that Mollie's not the type to give up, a sentiment her mom echoed on Friday.

"If it were me that were missing, Mollie wouldn't give up hope," she said. "You won't see me giving up hope. That's not an option."