Tens of thousands of Parisians flocked to the Place de la Republique on Wednesday night to denounce terrorism and the Charlie Hebdo massacre, and thousands more shared their horror and expressed support for the satirical publication on Twitter using the hashtag #JeSuisCharlie.

But supporters of Islamist militant groups also took to social media to celebrate the massacre — with Twitter fans of the Islamic State (IS) and al Qaeda (AQ) competing to use the buzz around the attack to push their propaganda.

French security forces continued to hunt for the unidentified suspects in the attack, who got away after the shooting. No group has so far claimed responsibility for the attack — the most deadly in France in decades. The attackers, who spoke fluent French, reportedly told the magazine's staff that they came from al Qaeda, with some reports specifically referring to al Qaeda in Yemen.

"The attack is certainly being talked about with approval in pro-IS circles, such as the prominent support account 'al-Nusra al-Maqdisia,'" Aymenn Jawad al-Tamimi, who has extensively researched Syrian and Iraqi militant groups, told VICE News. "Each side is hoping the attack was the work of their organization but I don't see anything that points to people with specific AQ affiliation in Yemen claiming the attack on social media."

The rivalry between al Qaeda and the Islamic State has lasted months, despite some attempts to reconcile the two groups into a united front.

France was already on high alert after a recent spate of so-called "lone wolf" attacks. On social media, supporters of the Islamic State, also known as ISIS, had reportedly called for attacks in Europe, and France in particular.

"ISIS supporters have been discussing coming good news for the brothers in Europe for some days," J.M. Berger, an analyst of extremism on social media, tweeted Wednesday.

Berger also noted that IS supporters on social media flocked to commenting on the attack quickly, "in a way they were not on Sydney," a reference to the siege of a café in Australia last month that left two people and a gunman dead.

"Top ISIS figures on social media [are] pushing users to make a run on the #CharlieHebdo hashtag, posting older propaganda with it," Berger added.

"Not to be outdone (OK, they are being outdone), al Qaeda supporters now running a hashtag on 'AQ invading France," he said.

Berger also noted that, "Charlie Hebdo has over its history offended a very wide range of people, not just jihadists," suggesting Islamic State and al Qaeda supporters weren't the only ones co-opting the hashtags.

He also credited a Twitter crackdown on pro-militant accounts for limiting the impact of their attempts to hijack the social media narrative.

Minutes before the attack, the Charlie Hebdo account had tweeted out a cartoon mocking the Islamic State's leader, Abu Bakr al-Baghdadi.

Meilleurs v? — Charlie Hebdo (@Charlie_Hebdo_)January 7, 2015

"Overall, I don't think there's enough evidence on social media itself that can point definitely one way or the other," al-Tamimi said, referring to the battle between ISIS and al Qaeda fans to take credit for the violence.

"On the one hand, the attack fits in with IS spokesman Adnani's call for IS supporters to target the French in particular," he added. "On the other, Charlie Hebdo was also on AQ's wanted list and AQ could bolsters its credibility with this sort of attack."

Either way, the social media voices of Islamic State and al Qaeda fans were largely drowned out by those that expressed horror and condemnation.