SAN FRANCISCO -- Rescuers Thursday evening suspended their search for a lost San Francisco sailor after four days of canvassing more than 132,000 square miles in optimal conditions, the U.S. Coast Guard announced.

At around 5:30 p.m., the Coast Guard called off intensive air and seaborne efforts to find 63-year-old Dr. Jim Gray or his vessel, the "Tenacious."

Initially covering parts of the ocean between San Francisco Bay and the Farallon Islands, searchers probed as far as 300 miles offshore, past the Oregon-California border to the north and as far south as the Channel Islands without any sign of the vessel or sailor.

"The decision to suspend a search is never an easy one and our hearts and thoughts are with Dr. Gray's family and friends during this time," said Capt. David Swatland, deputy commander of Coast Guard Sector San Francisco. "Although this search is suspended, if new information arises, it will be investigated."

The extensive search for Gray was inconclusive, although a fisherman reported seeing a boat with sails down in the area of Double Point Tuesday evening, according to Coast Guard Lt. Amy Marrs.

Communication with local mariners, harbormasters and officials at California marinas will continue through Sunday. Anyone with information on Dr. Gray or the vessel Tenacious should call (415) 399-3547.

Though the physical search has been suspended, the coast guard is joining forces with Gray's co-workers at Microsoft and using technology to try and find him. The Coast Guard says it has reason to believe that the Microsoft researcher was alive as late as 8 p.m. Sunday night, about a half hour before his family reported him missing.

The Coast Guard says at that time, Gray's PDA -- a personal digital assistant -- onboard his 40-foot sailboat Tenacious was syncing with his computer at work. Authorities are trying to use the Daly City cell phone tower to determine exactly where Gray was when the files were being downloaded.

"All that tells us is that the phone was on and near cell phone range, probably within 10 miles of the coastline. Had he immediately sailed south or north with no distress, he could be well south of the United States border, theoretically in Baja, California," said Coast Guard Lt. Commander Jonathan Copley.

Gray left Sunday morning for a trip to the Farallon Islands in his sailboat, reportedly to scatter his late mother's ashes, but failed to return when expected Sunday night, Marrs reported.

When Gray did not return that evening and did not answer cell phone calls, his wife called the Coast Guard at 8:35 p.m. to report his disappearance.

Gray is reported to have more than 10 years of sailing experience and his 40-foot boat, the Tenacious, is reported to have an Emergency Position Indicating Radio Beacon on board, according to Marrs.

Sergey Brin, co-founder and president of Internet search giant Google Inc., and engineers at online retailer Amazon.com sought high-tech ways to find the missing sailor.

Gray's work over the past 30 years allowed databases to sort quantities of information once considered too vast to manage, leading to the creation of both online shopping and Web-based mapping programs.

Brin explored whether recent satellite imagery provided for the company's popular Google Earth mapping software could be used to spot Gray's boat, a Google spokeswoman said.

Meanwhile, engineers at online retailer Amazon.com sought to ascertain whether the artificial intelligence software powering its Web site could be used to sift through aerial photographs of a wide swath of the Pacific.