JOHANNESBURG (Reuters) - Shares of Naspers fell more than 3 percent to four-week lows on Friday after China launched an investigation into its top social media sites, including the South African media company’s subsidiary Tencent’s WeChat.

The Cyberspace Administration’s investigation is the latest step in China’s push to secure the internet and maintain strict Communist Party control over content.

By 1221 GMT, shares in the South African e-commerce and Pay TV group were down 3.50 percent at 2745.51 rand, the weakest level since July 18 and putting them on track for their worst daily performance since early-July.

Shares of Hong Kong-listed Tencent, in which Napers owns 33 percent, fell almost 5 percent.

Naspers, a 1.2 trillion rand ($88.95 billion) multinational with private equity-style investments, owes much of its valuation to the $33 million investment it made in 2001 to take a stake in Tencent, which is now China’s biggest internet company with a $334 billion market capitalization.

Paul Chakaduka, a trader at GT247, said investors were waiting to see what steps the Chinese authorities would take.

“Unfortunately with the Chinese policy, it’s never clear cut....there’s lack of clear policy,” he said.

Beijing tightly controls its internet space and bans content that it deems politically threatening or damaging to China’s national identity. It has increasingly taken aim at the country’s booming internet industry.