ESTES PARK, Colo. -- Someone used a cell phone belonging to a missing exchange student two days after she was last seen, but investigators said Monday they had no other clues and did not know where she was.

Pratistha Budhathoki, 20, of Nepal was working in this town near Rocky Mountain National Park for the summer to help pay for her studies at St. Cloud State University in Minnesota, police said.

She was last seen when she left for work on June 18, but she did not arrive at her job, police Cmdr. Wes Kufeld said.

Kufeld said someone used Budhathoki's cell phone in Denver at 8:26 a.m. June 20 to check her voice mail. The signal came from Denver International Airport. He said investigators checked with airlines at DIA but no one recalled seeing her.

Kufeld said investigators also checked with hospitals around the state with no luck.

He said Estes Park has 17 sworn officers and all are working on the case. Estes Park is about 50 miles northwest of Denver.

An uncle of Budhathoki's is trying to travel to Estes Park but has been unable to leave Nepal because of visa problems, Kufeld said.

Police have said Budhathoki does not own a car and left her passport at home. She was not a hiker or mountain biker, police said.

Budhathoki is 5 feet 3 inches tall with black hair and brown eyes. She shared the apartment with friends from Nepal and didn't have a boyfriend or anyone else with whom she would have left unexpectedly, Kufeld said.

"She's not that kind of person. She wouldn't leave without informing anyone," said friend Sanbhya Khakyea.

"It's a big deal, if you think about it. You know, no phone call, nothing from her at all," said friend Aswin Pandey. "It kind of worries me a lot."