Sagiev has spent a lot of time walking and hiking in the park since arriving in June, and rangers are talking to his friends to find out what his routes and habits were, Skaggs said.
Co-worker Nicole Nicklas said Sagiev recently talked about planning a day trip to nearby Yellowstone National Park.
On Wednesday, searchers used dogs and boats along the Snake River near the resort but found no trace of Sagiev. On Thursday, searchers said Sagiev may have been hiking Taggart, Bradley or Delta lakes.
Rangers were methodically searching the area surrounding the privately owned resort, which includes cabins, shops and a gas station.
Dornan's is across the river from the park's headquarters and serves both visitors and residents. Many of its seasonal workers come from Eastern Europe.
It is unclear where in Russia Sagiev is from. His Facebook page says he was studying at the Higher School of Economics, which has its main campus in Moscow.
Sagiev is 5 feet 7 inches, has black hair, brown eyes and weighs about 155 pounds. He was last seen wearing tan shorts and a camouflage shirt.