The plaintiffs are four Black Lives Matter demonstrators, including the longtime girlfriend of slain protester Anthony Huber. Also killed that night was Joseph Rosenbaum.
The plaintiffs allege militia groups "collaborated, planned, orchestrated" an assault on protesters August 25. The defendants made it hard to "differentiate between the militias and police, who appeared to be working in coordination, the suit said.
Rittenhouse, 17, has been charged with intentionally killing Huber and Rosenbaum and wounding Gaige Grosskreutz. In a statement to NBC News, Rittenhouse's criminal attorney, John Pierce, said his client's actions were "classic self-defense." Rittenhouse has not yet entered a plea.
Rittenhouse was arrested in his home state of Illinois and is scheduled to have an extradition hearing Friday.
Attorney Lin Wood told CNN he represents Rittenhouse in his civil suits.
"As to Kyle Rittenhouse, this lawsuit is errant nonsense but may provide a golden opportunity for obtaining documents and sworn testimony from Facebook to bolster Kyle's future defamation case against Facebook for falsely accusing him of mass murder," Wood said. "Thus, I view the lawsuit as a blessing in disguise."
Facebook, the complaint alleges, provided the social media platform that allowed the groups to organize violence and declined to take action, even after more than 400 complaints were made about the Kenosha Guard.
A Facebook spokesman said, "We removed the shooter's Facebook and Instagram account and took action against organizations and content related to Kenosha. We have found no evidence that suggests the shooter followed the Kenosha Guard Page or that he was invited to the Event Page they organized."
The lawsuit includes screenshots of social media posts that help create a timeline of what happened in Kenosha, plaintiffs' attorney Jason Flores-Williams told CNN.
Kevin Mathewson, a defendant named in the suit who calls himself the "Commander of the Kenosha Guard," created a Facebook event page for the evening of August 25 called "Armed Citizens to Protect our Lives and Property," according to the lawsuit.
Mathewson's "call to arms," and his desire to "stand up to the evil thugs," was picked up by the alt-right media site InfoWars, the suit says. InfoWars gave the movement national attention, the suit says, emboldening and mobilizing individuals to "arm themselves and roam the streets" looking to intimidate and harass peaceful protesters such as his clients, Flores-Williams said.
Mathewson told CNN on Wednesday that he'd been advised by his attorney not to speak to the media. He would not provide the name of his lawyer.
The lawsuit says defendant Ryan Balch --a member of the Boogaloo Bois extremist group, according to the Southern Poverty Law Center's Hatewatch page -- described his involvement in the Kenosha protests in a Facebook post, saying he "joined a contingent of militia" in Kenosha and "inserted (himself) into a tactical advisement role." That group, according to the complaint, included Rittenhouse.
CNN couldn't reach
