Much of the empire built by Alex Jones, the Infowars founder and social media shock jock, vanished this summer when Facebook suspended Mr. Jones for 30 days and took down four of his pages for repeatedly violating its rules against bullying and hate speech. YouTube, Apple and other companies also took action against Mr. Jones. But a private Infowars Facebook group with more than 110,000 members, which had survived the crackdown, remained a hive of activity.

In Mr. Jones’s absence, the group continued to fill with news stories, Infowars videos and rants about social media censorship. Users also posted the sort of content — hateful attacks against Muslims, transgender people and other vulnerable groups — that got Mr. Jones suspended. And last week, when Mr. Jones’s suspension expired, he returned to the group triumphantly.

“My 30-day Facebook ban is up!” Mr. Jones announced.

Mr. Jones built his Facebook audience on pages — the big public megaphones he used to blast links, memes and videos to millions of his followers. In recent months, though, he and other large-scale purveyors of inflammatory speech have found refuge in private groups, where they can speak more openly with less fear of being punished for incendiary posts.

Several private Facebook groups devoted to QAnon, a sprawling pro-Trump conspiracy theory, have thousands of members. Regional chapters of the Proud Boys, a right-wing nationalist group that Twitter suspended last month for its “violent extremist” nature, maintain private Facebook groups, which they use to vet new members. And anti-vaccination groups have thrived on Facebook, in part because they are sometimes recommended to users by the site’s search results and “suggested groups” feature.