A study of how older teenagers use social media has found that Facebook is "not just on the slide, it is basically dead and buried", an expert says.
He claims it is being replaced by simpler social networks such as Twitter and Snapchat.
Young people now see the site as "uncool" and keep their profiles live purely to stay in touch with older relatives, among whom it remains popular.
University College London professor Daniel Miller, an anthropologist who worked on the European Union-funded research, wrote an article for the academic news website The Conversation.
"Mostly they feel embarrassed even to be associated with it," he said.
"This year marked the start of what looks likely to be a sustained decline of what had been the most pervasive of social networking sites.
"Young people are turning away in their droves and adopting other social networks instead, while the worst people of all, their parents, continue to use the service.
"Where once parents worried about their children joining Facebook, the children now say it is their family that insists they stay there to post about their lives.
"Parents have worked out how to use the site and see it as a way for the family to remain connected.
"In response, the young are moving on to cooler things.
"What appears to be the most seminal moment in a young person's decision to leave Facebook was surely that dreaded day your mum sends you a friend request."
The study observed people aged 16 to 18 in eight countries for 15 months and found that Facebook use was in sharp decline.
Young people were turning to simpler services such as Twitter, Instagram, Snapchat and WhatsApp, which Miller conceded were "no match" for Facebook in functionality.
"Most of the schoolchildren in our survey recognised that in many ways, Facebook is technically better than Twitter or Instagram," he said.
But "slick isn't always best" in attracting young users.
WhatsApp has overtaken Facebook as the number one way to send messages, said the researchers.
Snapchat has gained in popularity in recent months by allowing users to send images which "self-destruct" after a short period on the recipient's phone to maintain privacy.
Snapchat claims it handles 350 million images every day, and it reportedly turned down a US$3 billion ($3.7b) acquisition offer from Facebook.
Researchers found close friends used Snapchat to communicate, WhatsApp was used with acquaintances and Twitter broadcast to anyone who chose to follow that person.
The study found teenagers now used Facebook as a way to stay in touch with older members of their family and siblings who have left for university and had "evolved into a very different animal" from its early days as a social network focusing on young users at university.
Facebook, which will be 10 years old next year, is offering 70 million shares for sale at US$55.05 ($67.55) a share.
Forty-one million belong to founder Mark Zuckerberg and are being sold to cover a tax bill.