The authorities in China have detained a wealthy investor who went into business with relatives of the previous prime minister, a sign that the anticorruption campaign initiated five years ago by President Xi Jinping may again be closing in on a former top leader.

Duan Weihong, 49, who set up companies with relatives of Wen Jiabao, China’s prime minister from 2003-13, was detained before a Communist Party congress last year, according to three friends and business associates who spoke on the condition of anonymity for fear of reprisals by the authorities.

Ms. Duan, also known as Whitney Duan, was a central figure in a 2012 investigation by The New York Times that showed Mr. Wen’s relatives controlled assets worth at least $2.7 billion.

There has been no official acknowledgment of Ms. Duan’s detention, and it is not clear who detained her, why and whether she is still being held. Emails and phone calls to her offices were not returned.