The couple have been together for nine years

Patrick Kim McDermott, who was last seen at the end of June on a fishing boat, was ordered by a court in April to pay maintenance.

The US Coast Guard has not ruled out the possibility that the 48-year-old may have staged his disappearance.

Ms Newton-John has issued an appeal for information on his whereabouts.

"For those of us who know and love him, it has been a truly heartbreaking experience and we have chosen to deal with it privately," said the star of 1978 musical film Grease.

Personal effects

She has lived with camerman Mr McDermott for nine years, while his ex-wife reported him as missing a week after he was last seen.

Coastguards have said they are investigating all possibilities as to his whereabouts, but declined to comment on his financial situation.

Nobody saw Mr McDermott leave the boat, while his wallet and other personal effects were found onboard.

His car was found in the California marina where the overnight fishing trip set out from.

The court papers failed to clarify how much child support Mr McDermott owes, while according to a 1994 divorce ruling, his payments amounted to $800 (�442) per month.