Some surprising news is that according to the latest research in Japan, Facebook's users have started a decline. According to Cereja Technology, the number of Facebook users as of February 6 and 7, 2013 in Japan became 13,820,000, which is a 23.8% decline from January 2013. Cereja's research was based on the number of Facebook users when a company wanted to distribute a Facebook advertisement to Japanese users. According to similar research, the decline is mainly happening in the age range of 18 to 34.
It is not very clear why this kind of decrease has happened. One of the issues that may be relevant is the rise of a new SNS. It is not Google+, LinkedIn, nor Path. It is Line.
Line is a SNS operated by a Japanese entity of a Korean Company called NHN Japan. The company boasted having 100,000,000 users all over the world as of January 18, 2013. Of the 100,000,000 users NHN Japan claims that around 41,000,000 users are Japanese.
Line started from a smartphone App by which users can call for free (somewhat similar to Skype). But now it has a texting function and wall function similar to Facebook message and Facebook wall. It's growing popularity owes partially from the popularity of an unlimited data service plan for Japanese smartphone users and partially from the fact that Line made full use of the address book of the smartphone installed to help the user to get connected with other Line "friends".
It is not clear whether Line can replace Facebook in Japan. It is also possible that Japanese people are just using Line in some occasions and for some purposes and using Facebook in other occasions and for other purposes. Therefore, it is too early to conclude that Line's rising popularity has made young Facebook users logout from Facebook and turn to Line.
However, at least, as Facebook's ARPU (Average Revenue Per User) is not in the trend of rapid increase, it is important for Facebook to keep increasing the number of the users. I think there are two important points that we should pay attention to: (1) whether this trend of decline of the numbers of Facebook users in Japan continues and (2) whether other countries follow the Japanese trend.