Wellington, March 12 NZPA - Investigators looking into the collapse of an Auckland financial advisory firm believe at least $15 million is missing.

They have widened their investigation to include other businesses linked to Remuera couple Mike and Jackie Bradley.

Liquidators sifting through the accounts of B'On Financial Services, which traded as Bradley & Bradley, have identified 40 investors in Auckland, Kerikeri and Tauranga who are owed money by the firm, and believe there may be more who have not come forward, The New Zealand Herald reported today.

Serious Fraud Office head Adam Feeley said investigators had "significant concerns" about the Bradleys' business practices.

"Those concerns are such that we have now extended our inquiries beyond the original companies involved in the liquidation."

When the Herald visited Mr Bradley at home last week, he said the couple would prefer to wait "another couple of weeks" before talking to the media. He said the situation was "very complex".

The Companies Office began investigations last year after complaints from investors. Liquidators from BDO Auckland were appointed to four firms jointly run by the couple on December 21.

Last month BDO said the complaints regarded the whereabouts and existence of investment products purchased by investors over several years.

At that point investigations had indicated at least 36 investors who had invested about $12m with the group.

The primary activity of the companies appeared to have been financial planning, advisory and the placement of investor funds in products located principally offshore.