Police said there is no evidence of foul play in the missing case of Mackenzie Lueck.

Mackenzie Lueck's close friends all agree: She would never disappear after a late-night flight, leaving her cat alone and midterms unfinished.

Lueck, a 23-year old University of Utah student, returned from California to Salt Lake City Airport around 1 a.m. on June 17. She texted her parents that she landed safely, the Salt Lake Tribune reported.

Then she took a Lyft ride to the northern part of the city, far from where she lived, and vanished, police said.

A week later, Lueck's friends fear for her safety, and police scour for clues while being limited in their investigative powers.

"She threw a birthday party for her cat, so for her not to come home to her cat is not adding up," her friend Ashley Fine said in a Sunday news conference.

Police said that they have interviewed the Lyft driver and that the company was cooperative, but they have not discovered any information that would lead them to believe she was harmed or in danger.

Lueck was dropped off at a park in northern Salt Lake City, where she did not live, said police spokesman Detective Greg Wilking, who declined to say why she went there. That park is about a 20-minute drive in another direction from her home in Trolley Square on the eastern edge of downtown, Wilking told The Washington Post on Monday.

There is no evidence of foul play, which has restricted police from using investigative tools such as combing through Lueck's bank records and cellphone activity, said Sgt. Brandon Shearer, another police spokesman.

"Adults have the ability to not be found if they don't want to," Shearer said. However, Lueck was scheduled to return to California on Sunday but missed her flight, and that gives police "more cause of concern," which may lead to avenues such as a search warrant, he said.

Lueck's route "contained no irregularities" and ended at the scheduled destination, said Lauren Alexander, a Lyft spokeswoman. The driver continued on to pick up other riders, she said.

That has only compounded the mystery for Lueck's friends. Fine said she was unaware of Lueck having a significant other or any reason she would venture 20 minutes from her home.

Kennedy Stoner, her sorority sister, said it was "very unlike" Lueck not to check in with her.

"We don't believe she would miss a midterm because she was stressed. I am positive something is wrong," Stoner said. "I don't believe she would go off and not contact one person."

Lueck's friends have handed out missing person fliers and pleaded on Facebook for more information to assist the police.

"Kenzie, if you can hear this, we are all worried and we are looking out for you 24/7," Stoner said. "We are not able to sleep. I cannot sleep at night knowing you are out there. Please let us know if you are safe."