Updated

KALISPELL, Mont. — Authorities were searching Monday for a single-engine airplane carrying four people, including two Montana newspaper reporters, that took off the day before and did not return.

The 1968 Piper airplane departed from Kalispell City Airport on Sunday afternoon with Sonny Kless, the Missoula man who rented the plane, another Missoula man and two reporters for the Daily Inter Lake newspaper of Kalispell — Melissa Weaver and Erika Hoefer.

Weaver's roommate contacted the Flathead County Sheriff's Office and other agencies on Monday morning when Weaver had not returned or left a message.

Rick Weaver, publisher of the Daily Inter Lake, said the reporters were going on a sightseeing trip to Glacier National Park about 30 miles northeast of Kalispell.

"They were on their day off and just having fun," said Weaver, who is not related to Melissa Weaver. "We're just hoping for the absolute best. We hope that they're found, and everybody's OK."

Sheriff Mike Meehan told the newspaper that investigators believe the group was in the area of the park, but that was not confirmed.

Hoefer last updated her Facebook page about 10 minutes after taking off with a message reading, "We're flying to the park and we're later going to a barbecue," Meehan said.

Glacier National Park spokeswoman Amy Vanderbilt said there was no indication that the plane entered the park and that park officials were standing by to assist with the search.

Kless last made radio contact with the tower at Glacier Park International Airport at 2:11 p.m., about 40 minutes after takeoff, reporting that the plane was east of Kalispell, traveling north.

At least one text message was exchanged between Weaver and Hoefer's cell phones about an hour after that last contact, and a sheriff's detective was pursuing a subpoena to access that message from a server.

A state airplane checked wilderness airstrips after noon, Sgt. Ernie Freebury told the Daily Inter Lake. The Montana Civil Air Patrol joined the search along with a U.S. Customs and Border Protection helicopter.

The search area is very large and while the plane has a transponder on board, it's an old one, Meehan said. "You would have to fly almost directly over it to make contact, and that's a hindrance."

Authorities expanded their search Monday afternoon to include Lake County to the south and Sanders County to the southwest, sheriff's officials in those two counties said.

Freebury said officials also were analyzing radar data from Salt Lake City and cell-phone tower information.

The tail number on the airplane was registered to Joel Woodruff of Stevensville. A message left at a number listed for Woodruff was not immediately returned Monday evening.

Melissa Weaver, 23, is a police and courts reporter for the Daily Inter Lake. Her parents live in Billings and were headed to Kalispell, Rick Weaver said.

Hoefer, 27, is a business reporter for the newspaper who also writes for the Flathead Business Journal. She is from Beloit, Wis.

Both reporters began working for the newspaper at the end of last year.

The fourth person on board has not been identified.

(This version corrects year of aircraft, name of border agency.)