The age of 30 has become Facebook's largest user demographic.

Social media expert Michael McQueen, in what is described as the 'Levi's Effect', said teenagers were abandoning Facebook for other social networks such as Twitter, Instagram and Snapchat.

McQueen said Levi jeans were a cool, young brand until parents' started wearing them and the same thing has happened with Facebook, smh.com.au reports.

In 2012, Facebook was the primary social networking site for teenagers but this year Twitter has overtaken as the number one site.

McQueen said that as teens' log-off from Facebook, people aged 30 and over were logging-in.

He said that the older generation began signing up in 2010 as a lot of these users were parents who wanted to spy on their kids.

He added that now parents were logging in to reconnecting with old school friends and people who live overseas and they have caught the Facebook bug.

Professor of Public Communication at the University of Technology, Jim Macnamara, said adults also turn to Facebook while on holidays.