Use of Facebook among Americans aged 12 to 17 will fall 3.4% to 14.5 million this year, according to data from eMarketer – while 15.8 million in the same age group will use Snapchat.
In the 12-to-17 and 18-to-24 age brackets, Facebook’s user numbers will decline in the UK by 2.8% and 3.1%, respectively, this year, the report says.
Debra Aho Williamson, analyst at eMarketer, said the the milestone followed several years in which teens’ loyalty had shifted away from from Facebook, which now has more than two billion active users worldwide.
She said: "This year we finally felt comfortable saying, yes, this phenomenon is going on."
Facebook, with an estimated 32.5 million users this year, remains the most popular social network in the UK, but is losing share to Snapchat and Instagram among younger age groups.
More than a quarter of the UK’s population will log onto Instagram at least monthly by the end of 2017, eMarketer added.
However, longer-term growth prospects for Snapchat have now been lowered by eMarketer, which it said shows Instagram’s attempts to woo younger users with features similar to those of Snapchat are proving successful.
"Facebook is still the big winner in social media," Bill Fisher, eMarketer’s UK senior analyst, said. "But it will be slightly concerned that younger people in the UK are having their heads turned by Snapchat. Of course, its ownership of Instagram is softening the blow, and it will be further enthused to see Instagram’s longer-term prospects looking even better than Snapchat’s."
Meanwhile, Snapchat has now overtaken Facebook on "daily ad reach" among 13-24 year olds, the Financial Times reports.