According to a Nielsen survey Facebook had over 17.2 million Japanese users in May 2012

"According to the latest Nielsen/NetRatings survey, Facebook had 17.2 million Japanese users in May — and that figure has been steadily increasing. Mixi, by comparison, had about 20 million Japanese users."

Source: More Japanese users logging on to Facebook

Justin Lafferty

July 25th, 2012

http://allfacebook.com/japanese-users-facebook-mixi_b95488