The early stages of a search got under way Monday in the Flathead Valley area for a missing aircraft that was carrying two Daily Inter Lake staff writers and two men from Missoula.

The 1960 Piper Arrow, a blue-and-white single-engine airplane with a low wing, took off from Kalispell City Airport just after 1:30 p.m. Sunday. It had been rented by Sonny Kless of Missoula from North Star Aviation in Missoula and did not return to either the Missoula or Kalispell airports.

On board were Melissa Weaver, 23, a police and courts reporter with the Inter Lake, and Erika Hoefer, 27, a business reporter who also writes for the Flathead Business Journal. The second man on board has yet to be identified.

Weaver's car was still at the city airport on Monday morning; she and Hoefer were supposed to be at a barbecue with friends at 6 p.m. Sunday.

Their absence and lack of phone contact was considered strange by Weaver's roommate, prompting her to contact the Flathead County Sheriff's Office and other agencies Monday morning.

Sheriff Mike Meehan said the group was going on a scenic flight, mostly likely in the Glacier National Park area.

"We do have reason to believe they were in the park area, but we have not confirmed that," he said.

Sgt. Ernie Freebury organized an initial search, with a state airplane checking on prominent wilderness airstrips just after noon.

By Monday afternoon, several private aircraft with Red Eagle Aviation and the Montana Civil Air Patrol were involved in the search, along with a U.S. Customs Service helicopter that was detailed to the Western Governors Association conference in Whitefish.

Glacier National Park officials and the Montana Aeronautics Division also are engaged in the search.

"We were able to share with the sheriff that despite it being an extremely busy day, there were no reports or unusual sightings of aircraft," said Wade Muehlhof, a Glacier Park spokesman. "We're in standby mode making sure that the park's resources are available if requested."

Freebury said radar data from Salt Lake City was being analyzed along with cell-phone tower information.

Meehan said Hoefer last updated her Facebook page at 1:40 p.m. with a message reading, "We're flying to the park and we're later going to a barbecue."

The last voice message from any of the individuals' phones occurred at 1:51 p.m. However, there was text messaging between Weaver and Hoefer at 3:17 p.m., and a sheriff's detective was pursuing a subpoena late Friday afternoon to access that message from a server.

Kless last made radio contact with the tower at Glacier Park International Airport at 2:11 p.m., reporting that he was east of Kalispell, traveling south to north. It was unclear whether any type of flight plan had been left at any airport.

Freebury said the search area currently is very broad, but it will be narrowed.

"The problem right now is that … it is a very large area," Meehan added.

He said the type of plane involved was carrying an older-style transponder and bore the tail number N-7581J.

"It is our understanding that it's an old (transponder), and you would have to fly almost directly over it to make contact, and that's a hindrance," Meehan said.

Weaver, a University of Montana graduate from Billings, and Hoefer, from Beloit, Wis., both began work at the Inter Lake in December 2009.