It’s official: Facebook is for old(er) people. Teens and young adults are ditching Mark Zuckerberg’s social network as popularity among the over-55s surges, according to a report.

In 2018, 2.2 million 12- to 17-year-olds and 4.5 million 18- to 24-year-olds will regularly use Facebook in the UK, 700,000 fewer than in 2017, as younger users defect to services such as Snapchat, according to eMarketer.

A surge in older users means over-55s will become the second-biggest demographic of Facebook users this year.

The report says that while Facebook has so far been successful in keeping hold of younger users shifting to services such as Instagram, which it bought in 2012 for $1bn, defectors are now increasingly heading to upstart Snapchat.

“Facebook has a teen problem,” says Bill Fisher, UK senior analyst at eMarketer. “This latest forecast indicates that it is more than just a theory. Until now it has been able to rely on platform shifters being hoovered up by Instagram. However, leading the charge for younger audiences is Snapchat. There are now some early signs that younger social network users are being swayed by Snapchat.”

Fisher says that in the last three years Snapchat has more than doubled its take-up rate among UK users of social networking sites and apps to 43%.

The report reveals that as Facebook has grown older – the once spring chicken of the internet celebrated its 14th birthday earlier this month – so too has its user base, along with its popularity among older people.

The largest growth will be among older users, with 500,000 new over-55s expected to join Facebook this year. There will be 6.4 million 55- to 65-year-old-plus regular Facebook users this year, the biggest demographic save for 16- to 34-year-olds.

“There are a couple of factors at play here,” says Richard Broughton, an analyst at Ampere. “One is that older people tend to be late to the internet party, but adoption tends to find its way through the demographics eventually. And with Facebook’s video and photo experience it is a platform they want to be on to keep up with the social lives of their kids and grandchildren.”

Last month, Facebook announced a major overhaul of its news feed algorithm to prioritise what friends and family share, while reducing the amount of non-advertising content from publishers and brands.

Zuckerberg has pledged to spend this year “making sure that time spent on Facebook is time well spent”.

Last month, Facebook revealed a $4.3bn profit for the final quarter of last year, a 61% year-on-year rise.

Zuckerberg said 2017 proved a “hard one” for the company, which faced issues including its role in disseminating fake news and concerns it was used as a platform for Russian meddling in the US elections.

Overall, Facebook remains the most popular social networking site in the UK by some distance with 32.6 million total regular users this year. Instagram’s user base will grow from 15.7 million to 18.4 million, Snapchat will surge from 14.8 million to 16.2 million while Twitter will grow from 12.4 million to 12.6 million.