As of Wednesday afternoon, efforts to find Jeffrey May, 45, had turned up no sign of him, San Diego lifeguard Lt. Andy Lerum said. Searchers, including citizen volunteers helping municipal dive crews, planned to keep plying the waters and scanning the shoreline in the area until early evening, he said.May went to the northern San Diego beach early Monday morning, telling his wife he planned to meet up with a diving group, city lifeguard Lt. Greg Buchanan said. After May failed to return home or contact his wife again, she reported him missing about 8 p.m., Buchanan said.May's car was found in a parking lot in the area, and a plastic tub holding his car keys, sunglasses and clothing was located in a grassy area alongside the beach.On arriving in the area, May had rented a scuba tank and some diving weights at a nearby dive shop, but authorities could find no one who saw him entering the water.Lifeguards spent several hours Monday night searching from aboard boats and on shore vehicles, aided by a U.S. Coast Guard helicopter, before suspending the operation at about 11:30 p.m., Buchanan said.The effort resumed at 6 a.m. Tuesday. Almost three dozen divers from the San Diego Police Department and lifeguard agencies up and down the coast took part, along with the federal maritime agency's airborne personnel and the San Diego Harbor Police. The latter department deployed a vessel with sonar equipment, Buchanan said.The search turned up no sign of May, with the possible exception of a diving mask that could have belonged to him."It's an expansive search area because we have no idea what his last position was," said lifeguard Lt. Nick Lerma. To make matters worse, there may not have been anyone around if something went wrong. "It's one of the cardinal rules of scuba diving to dive with a partner," Lerma said. "To our knowledge, he did not have a partner and he did dive alone." 10News was told he went in with weights on which divers often do but that means if something went wrong, he would not float to the surface. Murky water conditions were making the job more challenging, Buchanan said."We can't see very much, which makes it that much more difficult," he said.May's wife told authorities her husband had been scuba-diving for 18 years. A friend of his, however, said May had not gone on a dive since last summer.May's wife said La Jolla Shores was one of her husband's favorite spots and he was familiar with the area.Tuesday's effort was suspended in the early evening. The municipal dive teams planned to continue searching the ocean in the area on Wednesday, starting at about 8 a.m., San Diego lifeguard Lt. Andy Lerum said.