Off the top of my head, a genocide, albeit by being careless people rather than malicious:

  The chairman of the U.N. Independent International Fact-Finding Mission on Myanmar stated that Facebook played a "determining role" in the Rohingya genocide.[98] Facebook has been accused of enabling the spread of Islamophobic content which targets the Rohingya people.[99] The United Nations Human Rights Council has called the platform "a useful instrument for those seeking to spread hate".[100]