A quarter of 18 to 29 year olds admit their use of social media such as Facebook, Twitter and YouTube has decreased, says Gartner.

According to the research firm, many of those that were using social network less than when they first assigned up claimed it was because they were "bored" with the sites, leading Gartner to suggest some web users are suffering from showing "social media fatigue".

"The trend shows some social media fatigue among early adopters, and the fact that 31 percent of Aspirers [younger, more mobile, brand-conscious consumers] indicated that they were getting bored with their social network is a situation that social media providers should monitor, as they will need to innovate and diversify to keep consumer attention," said Brian Blau, research director at Gartner.

Gartner also revealed that overall a third of social networkers are using sites less because of privacy concerns, although the research firm said attitudes to privacy are commonly age-related, with teenagers citing privacy concerns significantly less often than older respondents.

"The level of consumer concern around privacy will require ongoing vigilance for brands concerning customer opt-in and education. Lessons should be learned from the likes of Facebook as they test the boundaries of consumer tolerance in search of more revenue," added Charlotte Patrick, principal research analyst at Gartner.

In the UK overall, around 40 percent of social networkers said they use the sites more than when they first signed-up, while the same figure said they spend the same amount of time on social networks now as when they first joined. Just one in five said they use social networks less.