Analysts told CNBC this trend could get stronger this year, threatening to erode the social networking giant's dominance, although most said it would be hard to imagine a world where Facebook loses its crown completely.
"There is a real risk of social media fatigue, as evident from the fall in overall usage of social networking sites like Facebook and Twitter by average folks, and this is why leading companies like Facebook need to be forward looking in order to stay relevant," Sanjeev Kumar, at business management firm Delamore Consulting told CNBC.
At the end of 2013 researchers at digital consumer data provider GlobalWebIndex found that the number of U.S. teenagers active on Facebook fell to 56 percent in the third quarter of 2013 from 76 percent in the first quarter. The firm defines active usage as the number of users that have used or contributed to Facebook in the past month on any device.
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The rise of messaging apps
According to GlobalWebIndex, these disinterested teenagers are turning to messaging apps instead, with messaging app WeChat, video blogging site Vine and photo sharing site Flickr seeing the largest surges in popularity respectively.
When CNBC contacted Facebook the company disputed that it was losing popularity with its teenage user base.
"Overall teen usage has remained stable, and teens are among the most active users of Facebook. We remain focused on overall user engagement, including teens," a spokesperson for Facebook said.
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"Teens remain the most active users of Facebook and its clear they use multiple platforms – but Facebook remains a leader in a growing space," they added.
Still, Sendible's Hammar pointed out that if and when teenagers leave Facebook there's a risk the site will become less popular with other age groups as well, a trend he said was the central motive behind Facebook's acquisitions of photo blogging site Instagram in 2012, messaging app WhatsApp at the start of this year, and its attempt to buy photo messaging application Snapchat at the end of last year.
Hammer added that he too saw the rising phenomenon of social network fatigue as a key risk for Facebook, a trend some analysts have described as a weariness towards social networks in general, which is likely to lead to greater focus on privacy and contact between close groups of friends.
"With an increased number of ads appearing in the stream, it's becoming even more difficult for users to see what's important," said Hammar.
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"Facebook will continue to dominate. However, the time people spend on it will start to decline. The trend is moving to mobile and people are looking to connect more with the people they care about," he added.
One size does not fit all
Analysts told CNBC that the traditional idea of a 'one-size-fits-all' social network, like Facebook, where you have all your social networking tools centered in one place was now dying out.
"Generation Y and Z don't have any particular brand loyalty, and they're always on multi-platforms. All they want is the feature that's going to solve their problem right this moment," said Christian Ward, media and marketing editor at U.K.-based consumer lifestyle analysis firm Stylus.
Ward said privacy concerns are likely to continue to be an issue for major social networks this year, along with the limits surrounding freedom of speech.
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"Generation Y is constantly pushing the boundaries in this respect, and there's obviously a huge problem with abuse and bullying on Twitter and Facebook... It's my hope that there are some smart minds taking up this challenge right now, because it could be a real problem for the big players - and rightly so," he added.
Facebook is here to stay
Most analysts CNBC spoke to concluded that while Facebook's dominance of the social networking world is starting to look less solid, it's not likely its position at the top will be toppled anytime soon.
"The bottom line is that Facebook will continue to be a success for a long time to come but only if it keeps users happy at the same time as advertisers. This is a tricky balancing act, but one it's performing well at the moment," said Jon Myers, managing director for EMEA at Marin Software.
"Facebook should be the loser of 2014 but realistically it probably won't be," added Rachel Wood, Strategy Director, Partners Andrews Aldridge told CNBC. "It'll continue to dominate through corporate buy-outs rather than friendship, but its card is marked."