By Saad Sayeed

ISLAMABAD, Jan 18 (Reuters) - Families and supporters of five missing Pakistani activists on Wednesday denounced what they called a campaign to accuse the men of blasphemy, a highly charged allegation that could endanger their lives were they to reappear.

The accusations, made online and in a complaint to police, have unsettled Pakistan's small community of social activists.

The families of two of the missing men, Salman Haider and Waqass Goraya, described them as part of a "malicious campaign".

"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 two families said in a statement handed out at a press conference in the capital, Islamabad.

Associates and supporters of all five men deny they have blasphemed.

The liberal activists disappeared since Jan. 4, and some rights groups and newspapers have questioned whether state or military agencies were in some way involved.

Pakistan's Interior Ministry has said it is seeking information and the Federal Investigation Agency says it has not arrested them. Other state agencies and the country's military declined to comment.

Haider, a leftist writer and professor, disappeared in early January as did liberal bloggers Goraya, Aasim Saeed and Ahmed Raza Naseer, as well as Samar Abbas, head of an anti-extremism activist group in Karachi.

All were reported missing separately by their families within a week of each other.

In recent days, the missing activists have been accused of blasphemy in online posts and by at least three television commentators.

Haider Shah, of the Rationalist Society of Pakistan, said the blasphemy allegations endangered the activists.

Even if they were freed without charge, they could be targeted by extremists who believe violence is justified to defend Islam, he added.

"These people will be running from these allegations for the rest of their lives," Shah said.

In 2011, a Pakistani governor, Salman Taseer, was assassinated by his bodyguard after calling for reform of the blasphemy laws. His killer was hailed a hero by religious hardliners, and tens of thousands of supporters attended his funeral after he was executed last year.

POLICE REVIEWING COMPLAINT

One of the first blasphemy allegations appeared on Jan. 9 on the pro-military Pakistan Defence page on Facebook.

The anonymous Urdu-language post displayed photos of Haider, Goraya and Saeed linking them with a Facebook group called Bhensa, which it said contained "blasphemy toward the Koran".

When contacted by Reuters via email, an anonymous administrator for Pakistan Defence said the Facebook page and website were an "open source debate platform" and that comments were linked to members who "contribute anonymously".

The administrator added that, while many posts praised Pakistan's powerful military, the army was in no way associated with it.

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 Mohammad, a crime in Pakistan that carries a mandatory death sentence.

Tariq Asad, chairman of Civil Society of Pakistan, said the organization filed its police complaint in outrage after reading about the case.

"Every Pakistani has awareness of this issue and many have asked us to take this up ... Whoever does not love the Prophet, Peace Be Upon Him, more than his own family is not a true Muslim," Asad said.

Police officer Khalid Awan, based in Islamabad where the complaint was lodged, said it was under legal review, but so far formal criminal charges had not been brought.

Both Pakistan Defence and Civil Society of Pakistan dismissed suggestions that they were part of a coordinated campaign.

Critics of Pakistan's blasphemy laws say they have long been used by individuals and religious groups to settle disputes, but activists say that the accusations against the five signal a worrying escalation.

"The intensity of it is very worrying," said Shahzad Ahmed, director of cyber-security group Bytes for All.

"There is mainstream media, social media: the way it is being projected and repeated, the kind of force that they are using is unprecedented." (Editing by Mike Collett-White)

Our Standards: The Thomson Reuters Trust Principles.