The Serious Fraud Office is formally investigating a gold and precious metal trading company known as Bullion.Buyer.co.nz.
It says reports late last week of investors' concerns have resulted in others contacting the office.
SFO staff have secured the company's financial records and made additional inquiries.
As a result, the agency has concluded that there are reasonable grounds to believe that serious fraud may have been committed.
The SFO says its priority is now to contact as many investors as possible.
It will liaise with the Registrar of Companies to ensure steps are taken to protect funds for the benefit of creditors.