Gray, 63, hasn't been seen since last Sunday, when he sailed from San Francisco to scatter his mother's ashes near the Farallon Islands. There have been no signs of Gray or Tenacious, his 40-foot, red-hulled sailboat since.

    After the Coast Guard called off its weeklong search, Gray's numerous friends and colleagues in the high-tech world stepped in. They started an enormous private search that has volunteers working around the clock. A virtual army of tech workers is using satellite and software technology to scan images of the California coastline to try to locate Gray and his sailboat.

    Gray, who earned a doctorate in computer science from the University of California-Berkeley in 1969, made a call from his cell phone about 7:30 p.m. last Sunday, but so far no one has been able to pinpoint where it came from.

    Volunteers are working to get the phone company to find out what cell phone tower the signal came from. Searchers are also hoping that other sailors, harbor masters and coastal residents will be on the lookout for Gray and the craft.

    Employees at Amazon.com, along with scientists at Google, Microsoft and NASA, collaborated to come up with a way to scan thousands of satellite images of the vast California coast.

    Amazon.com engineers used imaging software to split photos from a DigitalGlobe satellite into smaller segments, then loaded them onto Amazon's "Mechanical Turk" website -- where volunteers and other "Friends of Jim" can scan them from their own computers.

    (Agencies)