For the past few years, social media in China has been dominated by the Twitter-like Sina Weibo, a microblogging service that created an online sphere of freewheeling public debate, incubating social change and at times even holding politicians accountable in a country where traditional media outlets are severely constrained.
But now, Weibo has been eclipsed by the Facebook-like WeChat, which allows instant messaging within self-selected circles of followers.
The shift from public to semiprivate communication, accelerated by a government crackdown on Weibo, has fundamentally reordered the social media landscape for the country’s 600 million Internet users, curbing what had been modern China’s most open public forum.
“This is a new phase for social media in China,” said Hu Yong, a journalism professor at Peking University. “It is the decline of the first large-scale forum for information in China and the rise of something more narrowly focused.”
Li Bo uses WeChat to rally opposition to damaging infrastructure projects. A chat account QR code is reflected in his glasses.
WeChat has its advantages and its defenders. It is less censored than Weibo, and some users say it allows them to speak more freely, knowing that their conversations are private. Many users relish its added functions, including voice messaging.
Last year in May, though, the government announced that WeChat would be more heavily monitored. Saying that instant messaging services were being used to spread “violence, terrorism and pornography,” the agency charged with policing the Internet said it would “firmly fight infiltration from hostile forces at home and abroad,” according to a government statement.
In its heyday, Weibo promised much more. It came to prominence in 2011 after a high-speed rail crash killed 40 people. Weibo users detailed the mayhem and government shortcomings that led to the accident. It was a signal moment in the Internet’s coming of age in China, a reminder of how the medium could challenge even a formidable authoritarian government.
Weibo is still important. Boundary-pushing news and commentaries are still more easily found there than in the more tightly controlled world of government newspapers and magazines. It also remains popular for following celebrities and gossip. It reported in March that it had 66 million daily users, up 37 percent over a year earlier.
But government figures show that the overall number of microblog users, including those using Weibo and services from other providers, fell by 9 percent last year, with many migrating to WeChat. That shift, along with a general decline in technology stocks, contributed to a disappointing New York stock market listing in April for Weibo, which raised $286 million instead of the anticipated $500 million.
“It’s far from what it used to be,” said He Weifang, a prominent lawyer and onetime heavy blogger on Weibo with more than a million followers. “You can still find facts on Weibo, or news reports, but the comments aren’t as interesting or deep.”
“现在比过去差远了，”著名律师及粉丝超过100万的热门博主贺卫方（音）说。“现在你仍可以在 Weibo 上发现事实，或者新闻报道，但是评论已不如以前有趣和有深度。”
One reason is the government crackdown on the so-called Big V accounts — prominent commenters, with verified accounts, who often had millions of followers. After hundreds were detained, most stopped posting on Weibo.
Others quit because of the sharp tone of commentary on Weibo, which often devolved into nasty, ad hominem attacks. Some grew tired of the dizzying list of banned terms and the cat-and-mouse games with censors to evade them.
WeChat seized on the frustration. Its parent company, Tencent, claims 355 million active monthly users. The company does not make public the number of daily users, making a direct comparison to Weibo difficult. But few people disagree that WeChat is now more popular.
More important, activists say, WeChat allows them to dig deeper into issues with like-minded people. The veteran environmentalist Li Bo has used WeChat for more than two years to rally opposition to damaging infrastructure projects, such as a controversial plan to dam the Nu River.
Mr. Li is a participant in one WeChat group called Environmental Policy Advocacy that has more than 300 members, including, he said, open-minded government officials. Although officials rarely participate, they see the traffic and occasionally invite members to their offices to chat about policies.
Some groups are smaller and narrower, such as one focused on a county in eastern China damaged by pollution. Others are task-specific, such as small committees for various campaigns and projects.
These groups can be powerful as long as they are not too overtly political. In late April, factory workers used WeChat to organize strikes against a Taiwanese company that had failed to pay into a retirement fund. Around the same time, however, churchgoers trying to use WeChat to prevent their church from being torn down found that their WeChat circles were being used to track down opponents of the government’s action.
A broader problem for activists, however, is that WeChat can become an echo chamber.
When a charity for coal miners was trying to raise $500 this year to buy oxygen pumps for a miner dying of black lung disease, its initial appeal fell flat. On a hunch, an employee, Xue Yinhu, appealed to followers on WeChat and raised the money in an hour.
“These people know you better, so they’re more willing to support you,” he said. “But sometimes you’re talking only to the same people.”
WeChat also has built-in constraints that hobble its ability to replicate Weibo’s public sphere. WeChat allows the creation of public accounts that anyone can follow, but limits posts to one a day. In addition, access to public accounts is not possible on cellphones, making it more difficult, for instance, to launch an incriminating photo of a public official into the blogosphere.
Comments are also deleted after a few days, making long-term discussions challenging and erasing a historical record. The government also monitors these accounts and recently deleted some covering social news and politics.
Tencent declined to comment on how it decided which functions to offer users.
Hu Jia, who has worked on environmental and public health causes for 15 years, said that the advent of social media, despite its limitations, had produced a better-informed society.
“Weibo and WeChat are gifts from God,” he said.