It's also one hell of a loaded term with things like Heavens Gate and Jim Jones having existed. To my knowledge, Facebook has yet to cause a mass suicide by people worshiping Zuckerberg.
Facebook has convinced millions of people to give up vast amounts of private information to an apparatus that would make the Stasi or KGB drool.
Part of cult indoctrination is giving up personal and private information, documents, secrets and property to participate and become part of the whole. Meanwhile, leaders profit from the property and information given up and use secrets to blackmail or breakdown an individual's identity so they become dependent on the group.