KCRG-TV(IOWA CITY, Iowa) — The family of a missing University of Iowa student now believes she is being held captive and has increased the reward for her return.An earlier lead about a possible spotting of 20-year-old Mollie Tibbetts, who disappeared on July 18 after going for a jog, has been ruled out, authorities announced Thursday.Mollie Tibbetts’ parents and boyfriend had a direct message for possible kidnappers at a press conference Thursday morning.“We believe that Mollie is still alive, and if someone has abducted her, we plead with you” to let her go, said Mollie’s mother, Laura Calderwood.“Everyday, I feel Mollie’s presence with me. Sometimes I just feel her sitting on my shoulder. 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.Police have ruled out Mollie Tibbett’s boyfriend, Dalton Jack, as a possible suspect. The two had been living together this summer.“If they’re listening, I would just like them to know imagine if this was you,” Jack said at the press conference.“Imagine if this was you. Somebody had taken your Mollie. Wouldn’t you want to help? Wouldn’t you want her back? Just do the right thing and let her go,” he said.Her father, Rob Tibbetts, said the $172,000 reward is “another tool in our arsenal.”“We are told very little by the authorities for very good reason,” he said, noting how police are hesitant to share information with anyone who could be connected to the case.“They’ve put together a very sophisticated investigation,” he said of the police.Authorities told reporters on Thursday that a reported sighting of the student more than 200 miles away in Missouri proved to be false.In spite of the unanswered questions in the case, “I do think she’s out there,” Rob Tibbetts said.“We’re setting our personal feelings aside. This is a fight for our daughter,” he added.Copyright © 2018, ABC Radio. All rights reserved.