The incident highlights rising risks posed to China's economy from its $2.6 trillion wealth management industry and the challenges it presents to regulators.

In a Hong Kong Stock Exchange filing posted on Thursday, Imagi International Holdings said it had not been able to reach Shan Jiuliang, the company's chairman and executive director, who also founded the Fanya exchange.

Imagi is not aware of Shan's whereabouts, said the statement. He was last seen at a board meeting on Oct. 15.

In July, hundreds of citizens protested outside the Fanya Metal Exchange in Kunming in southwestern Yunnan province, alleging the exchange had lost investments of more than 40 billion yuan ($6 billion).

A person who had worked at the exchange until recently told Reuters that authorities in November started asking Shan questions on trading numbers.

The source declined to be identified because she is not authorised to speak to the media.

The Fanya exchange and officials in the Kunming and Yunnan governments declined to comment.

The exchange, regulated by the local government in Yunnan province, trades 14 minor and rare metals, offering a range of investment products based on the metal stored in its warehouses.

($1 = 6.4798 Chinese yuan)

(Reporting by Engen Tham and Ruby Lian; Editing by Kazunori Takada and Tom Hogue)