According to the latest data, Sri Lanka has 16 Facebook users per 100 people. According to a 12,500 household survey conducted by the Department of Census and Statistics in January-June 2015, Sri Lanka has 11.8 Internet users aged 5-69 years, per 100 people. The wording is a little ambiguous, so it may be possible that it’s 11.8 households with a Internet user, per 100 households. If that is the case, we may still have more Internet users (more than one Internet user per household) than Facebook users. It’s also possible that Internet users have increased beyond 11.8% and even 16% in the months since the survey was completed.
But anyway, it seems that we are about to join South East Asia and Nepal in the group of countries where Facebook use > Internet use. If not right now, the trend seems to be that way.