The world’s biggest social network, Facebook, has an enviable position: it is ubiquitous with teenagers, a demographic group that is often elusive and fickle, but that at the same time is generally seen by marketers as one of the most important demographic groups out there.

In many cases, that is one of the reasons that marketers continue to pour more and more money into their Facebook marketing efforts despite the fact that many of them can’t precisely quantify what they’re getting in return.

To date, Facebook has managed to keep teenagers on side despite their historical willingness to move on to the next big thing. But if a survey of teenagers conducted by New York-based agency Mr. Youth is any indication, Facebook may have its work cut out going forward.

According to Mr. Youth’s survey, which asked 2,000 teens between the ages of 14 and 17 numerous questions about their Facebook use and what they like and don’t like about the social network, Facebook may be approaching the limit of attention it’s going to receive from this demographic group.

Just 4% of those surveyed indicated that they’d be spending more time on Facebook in the future. Just under half plan to spend the same amount of time on the site going forward.  

A significant minority (25%) claim they’ll be trying Google+ more and using Facebook less as a result. A double-digit fraction even say they plan to ditch Facebook completely.

While it obviously remains to be seen how many will follow through on their plans to spend more time on Google+, Mr. Youth says that some of the teens who have already made the switch feel feel that Google+ is “more social” than Facebook. Others laud the fact that the interface is cleaner.

Interface design, in a nutshell, seems to be the area where most of Facebook’s challenges with teens lie. Just 19% of those surveyed felt that Facebook’s recent interface changes were an improvement, and a little less than half expressed concern about the changes introducing clutter to Facebook.

The most hated addition to Facebook’s interface? The ticker, which one of the teens polled described as a “scrolling stalker.” On the flip side, it’s not all bad news for Facebook: teens who have tried it generally liked the new Timeline.

This highlights Facebook’s blessing and curse: there is still room for innovation, but it comes at a risk. Some new features will please, while others will confuse, disappoint and anger.

How Facebook balances the need to innovate with the risks posed by major changes is clearly going to be increasingly crucial. Clutter was a key contributor to MySpace’s downfall, and the fact that a considerable number of teens are voicing concerns about Facebook’s level of clutter should not be ignored by management.

At the same time, Mr. Youth’s survey also confirmed Facebook’s greatest asset: network effects.

As the agency discovered, “teens have opted for staying with Facebook over Google+ because the majority of their friends are already on it.” So long as Facebook can keep teens from fleeing en mass, it just might have far more leeway to conduct risky experiments with new features than just about any other consumer internet company before it.

That buys it time to convince its teenage users that the features it rolls out are useful and cool even if they don’t always appear that way at first glance.

The flexibility Facebook has, however, does not mean that Facebook should feel impervious to failure. Only one thing is stronger than network effects: the fickleness of teenagers. The world’s social network, which is run by someone who is now closer to 30 than 20, should respect that.