- Tencent, Baidu and Sina Weibo are being investigated by Chinese cyber-security regulators for potential violations
- Tencent shares in Hong Kong were down 2 percent on the day
An English translation of a notice on the office's website said the social media platforms of the three companies — WeChat, Tieba and Weibo respectively — have users spreading "violence and terror, false rumors, obscene pornography and other content that endangers national security, public safety and social order."
Citing earlier investigations, the notice said the platforms were "suspected of violating cyber-security laws and did not fulfill duties to manage information published by their users."
Tencent shares in Hong Kong were in the red following the news. The stock was down more than 2 percent following earlier losses of around 4 percent.
Baidu and Sina trade in New York and investors will be watching for any reaction at the U.S. market open.
CNBC's Barry Huang contributed to this report.