His nickname in China was “The Cannon,” and Ren Zhiqiang’s latest commentary was among his most explosive yet.

Mr. Ren, an outspoken property tycoon in Beijing, wrote in a scathing essay that China’s leader, Xi Jinping, was a power-hungry “clown.” He said the ruling Communist Party’s strict limits on free speech had exacerbated the coronavirus epidemic.

Now Mr. Ren, one of the most prominent critics of Mr. Xi in mainland China, is missing, his friends said on Saturday.

His disappearance comes amid a far-reaching campaign by the party to quash criticism of its slow, secretive initial response to the epidemic, which has killed over 3,100 people in China and sickened more than 80,000.