In building a case against him, the authorities have rounded up a number of Mr. Pu’s friends and associates, among them Vivian Wu, an independent journalist, and Xin Jian, a news assistant with the Japanese newspaper Nikkei. Friends say they are unclear why the authorities detained Ms. Xin, although some thought it might be related to an earlier interview she conducted with Mr. Pu.

On Tuesday, two weeks after her disappearance, Ms. Xin’s husband took to social media, posting a family photo and a frantic cry for help. “It’s a mess at home,” the husband, Wang Haichun, wrote. “Please come back. I can’t bear this alone.”

The anguish is shared by friends of Liu Wei, a young factory worker from southwest China who was detained on criminal charges on May 17 after returning home to Chongqing from a visit to Beijing. According to a friend, Huang Chengcheng, Mr. Liu’s apparent crime was posting online photos of himself in Tiananmen Square, including one in which he flashed a victory sign, a common pose among Chinese tourists that can also be seen as a sly act of subversion.

Gay rights advocates have also been feeling the heat. Over the past few weeks, the authorities have canceled a number of events in Beijing, including a film screening and a panel discussion to mark International Day Against Homophobia. Earlier this month, the police raided a hotel where a group of civil society advocates had gathered for a seminar focused on the obstacles facing gay and AIDS nonprofits.

Yu Fangqiang, one of the event organizers, said the police arrived at 1:30 a.m., confiscated his cellphone and then used it to text about 30 other would-be participants, telling them the event had been canceled. Mr. Yu and eight others were then bundled off for interrogations that, for several detainees, stretched into the following evening.

Sometimes the authorities’ fears of public unrest have led to confounding measures, like the postponement of a restaurant awards ceremony scheduled for Thursday night in the capital.

Other times their efforts were nothing if not creative.

Chen Yongmiao, a political commentator and rights activist in Beijing, said the police gave him the equivalent of $800 to leave town. “They just don’t want people from the opposition in the political center of Beijing,” Mr. Chen said by phone last week as he traveled through northwest China.