Facebook Reportedly Lost 2.8 Million US Users Under 25 And apparently, the research firm eMarketer says this year Facebook will lose even more. eMarketer found that the number of Facebook users in the U.S. between the age of 12 and 17 decreased by 9.9 percent in 2017. The firm released that the tech giant will lose about 2.1 million more users under 25 in 2018.