A missing sailor from the USS Shiloh who triggered a massive man overboard search in the Philippine Sea has been found alive on board the ship.

One week after he was declared missing, the sailor, Gas Turbine Systems Technician (Mechanical) 3rd Class Peter Mims, was found in the ship's engineering spaces, according to a U.S. official.

Mims (23) disappeared on June 8 while the Shiloh was operating 180 miles east of Okinawa. The U.S. Navy, Japanese Maritime Self-Defense Force and Japanese Coast Guard then spent over 50 hours and covered roughly 5,500 square miles looking for the sailor.

U.S. helicopters and aircraft, five U.S. ships, and three Japanese ships participated in the search, according to the Navy's 7th Fleet.

The search was suspended at midnight on June 11 and the Navy released the sailor's name, presumably after he was determined to have been lost at sea.

After he was found in the engineering spaces of the Shiloh on Thursday, Mims was transferred to the USS Reagan for a medical evaluation. The circumstances surrounding his disappearance are under investigation, a press release from the 7th Fleet said.

"We are thankful to have found our missing shipmate and appreciate all the hard work of our Sailors and Japanese partners in searching for him," Rear Adm. Charles Williams, commander, Carrier Strike Group 5 and Task Force 70, said in the statement. "I am relieved that this Sailor’s family will not be joining the ranks of Gold Star Families that have sacrificed so much for our country."

A separate U.S. official told ABC News that a sailor with Mims' title would know the ship's engineering spaces well. The official described those engine areas as tight with a lot of equipment and walkways for technicians.

When a sailor is believed to be unaccounted for, the ship's captain musters the crew to take attendance of everyone on board. If the sailor is not identified, a search of the ship is conducted, which this official said would have included the engineering spaces.

The Shiloh is a guided-missile cruiser that's about 567 feet feet long and 55 feet wide. These ships typically have thirty officers and 300 enlisted on board, according to the Navy's website.

PHOTO: The USS Shiloh, a U.S. Navy's Aegis-equipped destroyer, arrives at the port of Yokosuka, home to the Navy's 7th Fleet near Tokyo, Aug. 29, 2006. (Shizuo Kambayashi/AP Photo) More

The official would not speculate on what administrative actions Mims could face and stressed that the first priority was to get the sailor medical attention.

Mims' family says they are receiving hostile messages on social media. Shannon "Nicky" Mims, the sailor's sister, said people have called Mims' a "disgrace" and told her "the Navy has better things to do" than looking for her brother.

"It's supposed to be a time of rejoicing," she told ABC News. "Not getting hate mail."

She thanked the search parties for their time and wanted to send her condolences to the family of a USS Normandy sailor who was reported overboard off the coast of North Carolina last week.

Nicky Mims said her brother loves fishing, hunting, and working out.

A source close to the family, who preferred to remain anonymous due to the sensitivity of the matter, told ABC News that Mims, who is small in stature, was not treated well by the Navy and he "couldn't wait to get out."

According to this source, Mims only had a few months left of service.

"He always faces his problems," Nicky Mims said of her brother. "He never runs away from them."

Amy James, another of Mims' sisters, said she was relieved that her brother was found alive. She described Mims as "very strong-headed" with the ability to make anyone laugh.

"He's a very strong person, puts a smile on your face, helps anybody needing help," James said, adding, "He's a jokester."

Marie Mims, Mims' ex-wife, was also relieved, telling ABC News in a statement that "no one deserves to die young."

"I do feel like the Navy has explaining to do because the event of him going MIA had caused so much distress and sadness," she said.

"I know that Peter wouldn't hide in an engine room for no reason," Mims went on to say about her former husband. "He's a bright young man."

ABC News' Luis Martinez contributed to this report.