Mr McDermott has been missing since June

Mr McDermott has been missing since he was due to take a night fishing trip off the coast of California on 30 June.

His absence was only noted when he failed to turn up for a family get together on 6 July.

The 48-year-old cameraman has been involved with the Australian star of the 1970s film Grease for nine years.

Personal appeal

The coastguard was notified when Mr McDermott's car was found in a marina car park.

"It is under investigation," US Coast Guard spokesman Nathan Henise told AFP, adding that it was not clear if Mr McDermott had left the port on a boat or not.

Ms Newton-John found worldwide fame in the film Grease

"We are treating him as a missing person. We still don't know if he went overboard," Mr Henise added.

Ms Newton-John on Monday appealed for information concerning Mr McDermott.

"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."

Ms Newton-John is most famous for starring opposite John Travolta in the 1978 hit film musical Grease.