The overwhelming majority of teens in the U.S. are still actively using Facebook (META -13.80%). But it's hardly ever today that concerns investors -- it's tomorrow. That's why the Street is concerned about Facebook's third-quarter comment that there was a slight sequential decline in U.S. teen daily active users. Investors wondered: Could this be the beginning of the decline of teen usage on Facebook? In a recent interview with All Things D, Facebook COO Sheryl Sandberg's attempted to calm these concerns. Should investors listen?

Facebook's teen problem
Facebook shares may have gave a few investors heart palpitations in after-hours trading when the company reported third-quarter results on Oct. 30. In a matter of minutes, a 15% gain that followed better-than-expected results was completely erased. The culprit? A comment From CFO David Ebersman in the earnings call about teens is likely one of the factors that inspired the after-hour sell-off.

[W]e did see a decrease in daily users specifically among younger teens. We won't typically call out such granular data, especially when it's of questionable statistical significance given the lack of precision of our age estimates for younger users, but we wanted to share this with you now since we get a lot of questions about teens.

"Teens leaving Facebook?" The thought spooked investors.

Blown over?
Facebook COO Sheryl Sandberg told All Things D that she thought "the reaction to that comment has been blown out of proportion." Justifying why, she first reminded All Things D that "The vast majority of U.S. teens are on Facebook. And the majority of U.S. teens use Facebook almost every day." Next, she explained that Facebook simply won't always be the newest and coolest thing; short-term volatility in daily active users, therefore, is to be expected.

One of the challenges we face right now is that we're a decade old. That means that we're not the newest. And often, particularly in our space, newer things are shinier and cooler.

And what Mark [Zuckerberg] has said and what we all believe is that we're not trying to be the coolest. And we're not trying to be the newest. We're trying to be the most useful.

I think if you look at the way teenagers continue to use Facebook, we are useful to them.

She makes a great case as to why volatility like this might occur over time. And I would vouch for her case, reminding investors, as I've previously pointed out, that occasional declines in daily users among teens is almost inevitable at this point. As Ebersman said in the third-quarter earnings call, Facebook is "close to fully penetrated among teens in the U.S."

But I would care less to dub the Street's reaction to the news as an overreaction. In fact, I don't care to classify the reaction, period. Why? Because, over the long haul, this short-term volatility won't even matter. Just backing out three months, the stock is up 20%. Back out another six months and the stock is up 84%. Even more, with shares up so significantly, Facebook is trading at a whopping 17.7 times sales and a price-to-earnings ratio of 43.8. You can bet investors expect a rosy future for Facebook. And a rosy valuation on a hot growth stock sets the stage for unavoidable volatility. This short-term volatility will be voided meaningless as time passes.

What's the takeaway for investors? Breathe. While the Street overanalyzes every major price swing, Foolish investors should keep their eyes fixed on the horizon. The 10,000-foot view hasn't changed. Sure, investors should check in on the teen development next quarter. But for now, it's not worth anyone's time to discuss whether short-term volatility in a pricey growth stock is an overreaction or not. We're going to need more than one quarter's worth of data to really see whether this is a trend worth worrying about.

Will teen usage in Facebook in the U.S. begin to decline? It's simply too early to tell.