The Coast Guard says it is investigating the disappearance of Olivia Newton-John's (search) longtime boyfriend, who failed to return from an overnight fishing trip off the California coast seven weeks ago.

Patrick Kim McDermott (search), 48, left San Pedro, 20 miles south of Los Angeles, June 30 on an overnight fishing trip. The Los Angeles Police Department said McDermott has been listed as missing.

Coast Guard officer Nathan Henise told The Associated Press Monday that McDermott was last seen on the fishing vessel and that his personal items were found on the boat.

"We're treating it as a missing person case," Henise told the AP. "Everyone is being interviewed, everyone on the boat."

Newton-John on Monday urged anyone with information on his disappearance to contact authorities.

"I'm hopeful that my treasured friend is safe and well, and I'm grateful to the officials who are working so hard to find Patrick, whom I love very much," she said in a statement. "I ask anybody with information that could help to please please come forward."

Gavin de Becker, a spokesman for Newton-John, said the singer was in "close and frequent contact" with McDermott's family and friends, as well as investigators.

Authorities said McDermott's family became concerned when he didn't attend a July 6 event. They contacted the Coast Guard after his car was found in the marina's parking lot on July 11.

McDermott, a cameraman, and Newton-John, 56, have been together for nine years.

The singer appeared in the 1978 movie "Grease" opposite John Travolta.