The families of five missing Pakistani activists denounced what they called a "malicious" social media campaign accusing the men of blasphemy, a highly charged allegation that can have deadly consequences in Pakistan.
The five men had stood against religious intolerance and at times criticized Pakistan's military. They all vanished within days of each other earlier this month.
No group has claimed responsibility for their abduction and security agencies have denied involvement.
Meanwhile, the blasphemy accusations against the activists have been multiplying on Facebook and Twitter, triggering a flood of threats.
"This campaign can only be meant to divert public sympathy away from our plight and the plight of our loved ones, who have been illegally abducted," the families of Salman Haider and Waqass Goraya said at a press conference in Islamabad on January 18.
Haider, a leftist writer and professor, disappeared in early January along with liberal bloggers Goraya, Aasim Saeed, and Ahmed Raza Naseer, as well as Samar Abbas, the head of an antiextremism activist group in Karachi.
The missing activists have been accused of blasphemy not only in numerous online posts but also by at least three television commentators. One of the first blasphemy allegations appeared on January 9 on the pro-military Pakistan Defence page on Facebook. A site administrator said it was posted by an anonymous contributor.
Blasphemy is punishable by execution in Pakistan, and the allegations endanger the activists by making them and their families potential targets for vigilantes.
In 2011, a Pakistani governor, Salman Taseer, was assassinated by his bodyguard after calling for reform of the blasphemy laws. His killer was hailed as a hero by religious hard-liners, and tens of thousands of supporters attended his funeral after he was executed last year.
A group called Civil Society of Pakistan filed a police complaint over the weekend against the missing men, demanding that they be charged with insulting the Prophet Muhammad, a crime in Pakistan that carries a mandatory death sentence.
The society's chairman, Tariq Asad, said the organization filed the complaint in outrage after reading about the case.
"Every Pakistani has awareness of this issue and many have asked us to take this up," Asad told Reuters.
Both Pakistan Defence and Civil Society of Pakistan dismissed suggestions that they were part of a coordinated campaign.
Activists said that the blasphemy accusations against the five were worrying, and have filed a countersuit demanding that they be halted. They said the online campaigns are intended to silence progressive voices and are carefully coordinated.
The accusations have already prompted several liberal online commentators to close their social media accounts, activists said.
"The intensity of it is very worrying," Shahzad Ahmed, director of cybersecurity group Bytes for All, told the Reuters news agency.
"There is mainstream media, social media: the way it is being projected and repeated, the kind of force that they are using is unprecedented."
With reporting by AFP and Reuters