Chen Qiushi was reported missing by his family on Thursday – a few hours before the death of whistleblowing doctor Li Wenliang – after setting off to one of the new makeshift “square cabin” hospitals in Wuhan.
His mother posted videos on social media making a public appeal for information after he failed to respond to calls or messages.
“Chinese citizen journalist Chen Qiushi has been missing since 6 February,” the family tweeted in a message to Donald Trump and other US politicians. “He travelled to Wuhan to report on the coronavirus outbreak.
“His family and friends are deeply worried. Please help to spread the news and support him.”
Mr Chen, who has 250,000 followers on Twitter, had previously posted videos about eight health workers who were reprimanded by police for speaking out about the coronavirus outbreak.
Authorities later told Mr Chen’s mother that the journalist was being detained in quarantine at an unidentified location, according to reports.
The family’s last Twitter post on Monday morning repeated their public appeal under the hashtag “FindQiushi”.
It included a video clip of the Chinese ambassador to the US, Cui Tiankai, being asked whether Mr Chen had been detained.
The ambassador replied: “Sorry I have never heard of this person.”