Sgt. Cindi West says about 75 members of the sheriff's search and rescue unit looked for the man for hours Thursday.
A helicopter pilot reported about 2:30 p.m. that a skydiver had jumped from the aircraft but failed to show up at a landing zone near Mount Si, about 30 miles from Seattle.
"Our hope is that he got stuck in a tree or maybe injured his leg or something and is just waiting for somebody to come rescue him," West said.
The pilot said three men were alternating going up in the helicopter to jump, with one jumping while the others waited at the landing zone.
The pilot said the men were jumping from about 6,500 feet. West says the line of sight was blocked for the men at the landing zone so they did not see their companion jump.
Glenn Wallace was one of the search and rescue volunteers. His crews used all-terrain vehicles to drive up trails nearby. While they didn't find the man, they were prepared to keep him alive.
"If someone's in trouble, we want to find them, get them to safety and get them to warmth and medical attention," Wallace said.
West says the 29-year-old missing man is from Florida. No additional information was released about him, the pilot or the other skydivers.