No one is believed to have survived.
The search has been suspended for the night, but will resume Sunday on the ground.
Reported missing are Michael Bybyk, 75, and Joyce Bybyk, 70, both of Fullerton, Alvin Baker, 79, of Chino, and Gail Pugel, 68, of Ontario. The missing plane, owned by the Bybyks, is a white twin-engine Cessna 340, tail number N354TJ, Chino police said.
Family members reported the four missing late Wednesday night. Aerial searches Thursday and Friday in the San Gorgonio Pass and near Mount San Jacinto have turned up no sign of the Cessna 340, said Chino police Lt. Al Cheatham.
Authorities Saturday hope a third successive day of clear weather in the mountains increases their chances of spotting the missing plane.
"The plane is very light gray and white, difficult to spot in snow," Cheatham said. "We haven't assigned any ground crews yet, as far as I know. The terrain there is extremely steep and rugged."
Investigators believe the Bybyks, Baker and Pugel left Chino Airport the morning of Feb. 2 and flew to Bermuda Dunes Airport near Indio. They took off from Bermuda Dunes to return to Chino at about 1:30 p.m., Cheatham said.
Last contact with the plane was at 1:39 p.m. in the area east of Banning near the San Jacinto Mountains, authorities said.
"The last radar reading puts them in the San Gorgonio Pass," Cheatham said. "They were also seen by occupants of another plane going into a bank of clouds."
Investigators believe Michael Bybyk was piloting the plane, Cheatham said. Bybyk has been certified for single-engine and multi-engine aircraft since May 1992, according to a Federal Aviation Administration database.
"We are concerned because the storm came in that night and Sunday," Cheatham said. "Snow was already reported 10 to 12 feet deep in some places above 7,000 feet elevation, and the storm dumped more snow."
Civil air patrol volunteers are conducting another aerial search Saturday, along with pilots with Riverside County sheriff's aviation and San Bernardino County sheriff's aviation, Cheatham said.
Mountain search-and-rescue volunteers were busy through the storm last weekend. On Sunday, ground crews managed to rescue two Marine sergeants from Twentynine Palms who attempted to ascend an ice-encrusted trail near the Palm Springs Aerial Tramway.
On Monday, a helicopter team rescued a Riverside woman who summited Mount San Jacinto on Saturday, slipped and broke an ankle, then spent two bitter-cold nights in a stone hut just below the peak.