At dusk on Tuesday, there still was not a trace of a plane missing since Sunday with four people on board

Lake County Sheriff Lucky Larson briefed a group of family members and friends around 8 p.m., addressing a rumor the search was being called off.

“We’re not quitting,” Larson told a weary group of about a dozen people at the visitor center at the National Bison Range 80 miles south of Kalispell.

“We want to find them.”

The search will resume at 6:30 a.m. today and Larson offered to meet family members of the missing foursome at 8 a.m. at the Polson Airport, where the aerial search is being coordinated.

Larson also brought family members into the search command center Tuesday night to meet with Sanders County Undersheriff Rube Wrightsman to go over maps of the search area and answer questions.

According to Wrightsman, Tuesday’s search involved 10 airplanes, five boats, all-terrain vehicles, a team on horseback and three or four helicopters.

Wrightson and Larson assured the group that a similar effort will be mounted today.

The plane that left Kalispell City Airport on Sunday was carrying four people: Inter Lake reporters Melissa Weaver and Erika Hoefer, both of Kalispell, and two Missoula men, pilot Sonny Kless and Brian Williams.

The search had shifted somewhat Tuesday toward the lower Flathead River west of the National Bison Range.

By midafternoon, at least four boats fitted with sonar equipment searched the lower Flathead River between the town of Dixon and the river’s confluence with the Clark Fork River.

Search officials stressed that an extensive aerial search continued, too, over a much broader area.

“Who knows? In just a matter of minutes, it could be miles and miles from the river,” said Carey Cooley, a public information officer for the Lake County Sheriff’s Office.

Larson said roughly 100 people are involved in the official search, plus many friends and family members of those on the plane are searching as well.

The focus on the river is because of eyewitness accounts.

“The one thing that has been consistent is that they [witnesses] have seen a blue-and-white aircraft flying low over the Flathead River,” Cooley said.

The 1968 Piper Arrow, a blue-and-white single-engine plane, last was tracked by radar at about 300 feet above ground level west of the Bison Range at Moiese.

It went off the radar screen at 4:02 p.m. Sunday, Flathead County Sheriff’s Sgt. Ernie Freebury said.

Federal Aviation Administration radar data showed the airplane had traveled from Kalispell north along the Whitefish Range, entered Glacier National Park airspace, then headed south along the Swan Mountain Range and flew across Flathead Lake to the Bison Range, Freebury said Monday.

The river search also involves the river banks and some islands. “They are checking those islands as well,” Cooley said. “They are very brushy.”

The plane and its occupants had been missing from a Sunday afternoon sightseeing flight.

“We had folks in vehicles and four-wheelers search throughout the night,” Cooley said from the search command post at the National Bison Range.

Aerial search efforts ramped up Tuesday morning.

“Our base starting point is that last radar contact,” Cooley said. “That’s where we started.”

Cooley said there have been several eyewitness reports from people who saw the plane flying low just west of the Bison Range.

“There’s a consistency in those reports where everybody said the same thing: ‘It was flying low,’” Cooley said. “They [searchers] are using those reports and going out from there.”

The Flathead River flows about three miles west of the Bison Range. The river bottom is lush with cottonwoods and brush.

The terrain in the area is mostly open, prairie-grass-covered rolling hills ringed by timber-capped mountains.

The pilot, Kless, last made radio contact with the tower at Glacier Park International Airport at 2:11 p.m. on Sunday, reporting that he was east of Kalispell, traveling south to north.  

Freebury said cell-phone tower information also was analyzed.

Flathead County Sheriff Mike Meehan said Hoefer last updated her Facebook page at 1:40 p.m. with a message reading, “Flying over Glacier in a private plane then off 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 3:47 p.m.  

“The last text they sent pinged off the Ronan tower,” Freebury said. “That was our second confirmation, besides the radar data, that they were in that area.”

Meehan said the type of plane involved was carrying an older-style transponder and bore the tail number N-7581J. The plane is registered to Joel Woodruff of Stevensville.

“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, from Billings, and Hoefer, from Beloit, Wis., both began work at the Inter Lake in December 2009.

Weaver is the daughter of Daniel and Katherine Weaver of Billings; Hoefer is the daughter of William and Candy Hoefer of Beloit.

Kless is a recent graduate from the University of Montana with a degree in environmental studies and communications. Williams attends law school at the University of Montana.