The reality: The number of U.S. Facebook users in the 12- to 17-year-old demographic declined by 9.9 percent in 2017, eMarketer found, or about 1.4 million total users. That’s almost three times the decline expected. There were roughly 12.1 million U.S. Facebook users in the 12- to 17-year-old demographic by the end of the year.

Source: Facebook lost around 2.8 million U.S. users under 25 last year. 2018 won’t be much better. – Recode