Crimestoppers of Central Iowa, which offers a line for anonymous tips, helped to organize the press conference and will administer the reward money.
As of 10 a.m. Thursday, $172,000 had been raised, Calderwood said.
But he said, "I'm confident we have a solid timeline that we're working on" - though he added that they weren't releasing that information just yet.
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Investigators are still looking for clues in the disappearance of 20-year-old University of Iowa student Mollie Tibbetts.
"Mollie was a friend to everybody", said Kim Calderwood, her aunt. "And Mollie was an incredibly strong young woman and I don't know that I have the strength in me and Mollie is lending me her strength every day and every night", she said.
Her family reported her missing the next day after she didn't show up to work.
He also made an appeal should someone be holding his daughter.
"That tipster then will have to. contact us back if a crime has been solved", he said.
She announced an A$233,000 reward for her return.
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, with the help of Federal Bureau of Investigation forensic experts, were tracking Tibbetts' digital footprint.
Police say Tibbetts was last seen wearing dark colored running shorts and running shoes. "Unfortunately, we have not found Mollie", said Kevin Winker, Director of Investigative Operations for the Iowa Department of Public Safety.
The avid runner stands at 5-foot-3 and weighs 120 pounds.
The girl's family is expected to speak to the media Thursday and investigators are expected to provide an update Friday.
Mollie Tibbetts was last seen jogging on the evening of July 18 in Brooklyn, a small town in Iowa where she had been living over the summer. Officials continue to search for her.