The China Internet Network Information Center said in an annual report Thursday that there were 281 million users of Twitter-like microblogs such as Sina Weibo at the end of 2013, down 9 percent from the previous year. It also reported an overall decline in users of social media as a percentage of the entire population of Internet users.
"I think there are several reasons, with the crackdown being one," said Willy Lam, a political analyst at the Chinese University of Hong Kong. "People don't want to get into trouble, and they have found other means of communications."
One prominent alternative is WeChat, a mobile instant-messaging service that has risen in popularity since 2012 and has threatened the dominance of Sina Weibo in information sharing.
Statistics from the information center show that mobile instant-messaging services experienced rapid growth in 2013, adding 78.6 million users, or 22.3 percent.
The field leader is WeChat, which allows users to share information within circles of friends or open a public account that others can subscribe to, similar to the Twitter feature of having followers, but without a word limit.
The decline in online social media, especially in microblogging — known in Chinese as weibo — was palpable last year, following a heavy-handed government campaign against what it considered rumors, negativity and unruliness in online discourse. A new legal interpretation allows the government to jail microbloggers who post false information that has been reposted 500 times or viewed 5,000 times.
"It has squeezed off some bubbles, and people have become more cautious in forwarding messages," said Shen Yang, a professor of information management at Wuhan University in central China.
"At its heyday, the viewpoint was that weibo could change everything, but it overlooked the transformation China could have on it."
The government shut down numerous microblogging accounts and arrested dozens of microbloggers on the charge of spreading rumors or unrelated charges, in a campaign observers said was aimed at stifling criticism of the government and ruling Communist Party.
By late 2013, governments at all levels and state media had a major presence on China's microblog sites in a concerted effort to control the public discourse there.
In November, a top propaganda official declared a victory when asked to comment on the state of China's formerly vibrant microblog-sphere.
"If we should describe the online environment in the past as good mingling with the bad, the sky of the cyberspace has cleared up now because we have cracked down on online rumors," said Ren Xianliang, vice minister of the State Internet Information Office.