When Mr. Alefantis discovered that his employees were getting similar abusive messages, he looked online to unravel the accusations. He found dozens of made-up articles about Mrs. Clinton kidnapping, molesting and trafficking children in the restaurant’s back rooms. The articles appeared on Facebook and on websites such as The New Nationalist and The Vigilant Citizen, with one headline blaring: “Pizzagate: How 4Chan Uncovered the Sick World of Washington’s Occult Elite.”

None of it was true. While Mr. Alefantis has some prominent Democratic friends in Washington and was a supporter of Mrs. Clinton, he has never met her, does not sell or abuse children, and is not being investigated by law enforcement for any of these claims. He and his 40 employees had unwittingly become real people caught in the middle of a storm of fake news.