On May 8, 2015, at 0115 Pacific daylight time, a Cessna 172S, N191TG, departed Palo Alto Airport of Santa Clara County (KPAO), Palo Alto, California, en route to an unknown destination. Since that time, the commercial pilot, the sole occupant of the airplane, has not been located and the airplane is missing and is presumed to have crashed in the Pacific Ocean. Night visual meteorological conditions prevailed for the flight. The airplane was registered to Tango Golf Aerospace and leased back to Advantage Aviation. On May 8, a representative from Advantage Aviation contacted the Palo Alto Police Department and reported that the airplane and pilot were missing. The representative reported the missing pilot was a contract flight instructor with Advantage Aviation, but stated that the flight in question was not scheduled, dispatched or authorized. The Palo Alto Police Department later classified the airplane as stolen. Recorded radar data was obtained from the Federal Aviation Administration. Radar returns believed to be N191TG began at 01:14:41. The radar data showed an aircraft on a 1200 transponder code departing from the Palo Alto Airport and tracking generally westbound to the Pacific coast about 5 miles southwest of Half Moon Bay, California. The aircraft then turned left and followed the coastline. The last transponder return was recorded over the water about 5 miles west of Davenport, California, at 01:41:06. The aircraft was indicating about 800 feet above sea level. A primary target with no altitude information was then seen executing a series of maneuvers in the vicinity. At 0215, primary targets consistent with N191TG began heading away from land on a true course of about 220 degrees. The targets continued straight ahead until no longer visible to radar. The last primary target was seen at 36.343N, 123.196W at 0243 PDT. N191TG was equipped with a 406 mHz emergency locater transmitter (ELT) registered to the aircraft. According to the Air Force Rescue Coordination Center, a single transmission with no associated location information was received from the ELT at 0424 PDT by a search-and-rescue satellite. The U.S. Coast Guard conducted a search for the missing airplane and ramp checks were conducted at several airports along the apparent route of flight; however, no wreckage was found. The airplane and pilot remain missing.