"We hoped for broad support, but the number ... has exceeded my most optimistic expectations," said Austrian law student Max Schrems, who launched his class action only last Thursday.
Schrems, 26, has enlisted the public to help him take on Facebook, a U.S.-listed company worth $189 billion with 1.32 billion users across the globe.
"With this number of participants, we have a great basis to stop complaining about privacy violations and actually do something about it," he said in a statement.
Schrems said he had closed the list of plaintiffs because his legal team needed to verify and administer each claim that Facebook users submitted. Others can still register at www.fbclaim.com should the class action expand later.
Under Austrian law, a group of people may transfer their financial claims to a single person - in this case, Schrems. Legal proceedings are then effectively run as a class action.
Schrems is claiming damages of 500 euros ($667) per user for alleged data violations by Facebook, including by aiding the U.S. National Security Agency in running its PRISM programme, which mined the personal data of users of Facebook and other web services.
Austrian law is generally favourable to data privacy, but Schrems is also seeking injunctions under EU data protection law at the court in Vienna.
Schrems already has a case involving the social network pending at the European Court of Justice in Strasbourg, France.
Facebook, which has declined comment on Schrems's campaign, has been accused before of violating data protection laws.Most recently, Britain's data watchdog has begun investigating the legality of a Facebook experiment on unwitting users in 2012, in which it altered their feeds to see if changes in the amount of positive news they were shown had an influence on the positivity of their postings.