"I feel like something is terribly wrong," friend Stacy Morris told ABC7. "We're pretty much worried that she might be dead and that she's not going to be able to come home to her kids and her sister."
Schmidt said her sister’s driver’s license and Social Security card were found on a bus in Denver. Vandewiele sent her sister a selfie taken near Union Station.
The rest of Vandewiele's belongings were found in a motel room in Denver, according to WQOW in Eau Clair, Wisconsin.
Schmidt told the Wisconsin news station that Vandewiele spoke to a friend over the phone on July 23 and said she would call the following day -- if she was still alive. Vandewiele, who suffers from anxiety and depression, also said she was scared for her life and that she never should have gone to Colorado with Mayer, the news station reported.
"I guess we have no reason to believe that there was any foul play," Dunn County Sheriff Dennis Smith told WQOW. "But, we don't have any reason to believe that there wasn't any foul play."
The Denver Police Department is leading the investigation into Vandewiele's disappearance. Denver police officials describe her as 5 feet, 5 inches tall and weighing about 120 pounds.
Vandewiele has brown eyes and long brown hair. She also has a tattoo on her forearm that reads, “I do what I want.”
Anyone with information on her whereabouts should call Denver investigators at 720-913-7867.