Rescue crews spent their fourth straight day looking for a skydiver who vanished during a jump above Washington's Cascade foothills, but found no sign of the Florida man by dusk.

King County sheriff's Sgt. Cindi West says 100 searchers were out near 4,200-foot Mount Si east of Seattle early Sunday to find 29-year-old Kurt Ruppert of Lake City, Fla.

Ruppert hasn't been seen since he jumped out of a helicopter at 6,500 feet Thursday afternoon, wearing a special wing suit with fabric under the arms to allow him to glide like a flying squirrel.

Crews narrowed their search area Saturday, based on data from Ruppert's cell phone and the helicopter's flight path.

It wasn't immediately clear whether the search would continue Monday.