Facebook (NASDAQ:FB) has overcome the problems that plagued its initial public offering to become a steadily growing force in the stock market.

The company's stock price has been driven by its revenue growth, specifically its ability to monetize mobile users. Revenue exploded in 2014, growing 58% to $12.47 billion. Perhaps even more impressively, Facebook managed to grow its user base in every facet of its business.

Here are some examples:

  • Daily active users were 890 million on average for December 2014, an 18% year-over-year increase.
  • Mobile DAUs were 745 million on average for the same month, a 34% year-over-year increase.
  • Monthly active users were 1.39 billion as of Dec. 31, a 13% year-over-year increase.
  • Mobile MAUs were 1.19 billion as of Dec. 31, a 26% year-over-year increase.

Despite becoming ubiquitous and moving from hip technology to a place your grandmother hangs out, Mark Zuckerberg's company has so far managed to escape the cliff that has befallen every other social-media play in history. Facebook is growing rapidly, as its stock price suggests:

FB, data by YCharts

But while Facebook the company and Facebook the stock have been flying high, the same things that brought down MySpace, Friendster, Digg, and so many others could crash Zuckerberg's brainchild. Facebook is not a stock that will crater because of a bad quarter of advertising sales, but it is one that could face quick difficulties if public interest in the social-media platform craters.

It could happen
While Facebook is bigger than MySpace ever was, the still-alive-but-no-longer relevant platform provides the best comparable for how quickly and spectacularly the mighty can fall. At its peak in December 2008, MySpace had 75.9 million monthly unique visitors in the U.S., according to comScore. That's a relatively small number compared with Facebook's 890 million MAUs in December, but the Internet itself was a much smaller universe in 2006.

MySpace's fall was quick but not immediate, as the company fell to 34.8 million monthly unique visitors as of May 2011.

"MySpace makes nearly all its money from advertising; the exodus has a direct correlation to its revenue," BusinessWeek reported in 2011. "In 2009 the site brought in $470 million in advertising dollars, according to EMarketer. In 2011, it's projected to generate $184 million."

The numbers are all fractions of what Facebook brings in, but the reason for the decline should put at least a twinge of doubt into the social-media network's shareholders. MySpace failed because Facebook (and, to a lesser extent, Twitter) came along. Something newer, cooler, and more useful made MySpace -- once the social-media site touted by popular musicians and radio hosts alike -- irrelevant.

It's hard to picture the same fate for Facebook because the site is so dominant, but giants can fall. Facebook's revenue and stock price are still driven by ad sales, which are dependent on visitors.

Zuckerberg knows this
Facebook's leader didn't miss the lesson of MySpace or any of his company's other social-media predecessors. He's learned the lesson of how quickly a site can go from dominant to irrelevant, and Zuckerberg has been racing to give Facebook other options.

This initiative has been somewhat successful, at least from an audience point of view. Facebook spun off its Messenger app from its main Facebook app, which gives the company two of the top apps in the United States. In addition, the company's $19 billion acquisition of the WhatsApp messaging platform gives it yet another product with the potential to serve over 1 billion global customers.

Zuckerberg also bought Oculus, which brings virtual-reality technology that might prove very lucrative.

All of these are potentially huge businesses, and all offer a hedge against a new, cooler social-media platform that could supplant Facebook. But none of them are being monetized at anywhere near the level the main Facebook site is.

That's not to say they won't be. Zuckerberg's impressive efforts to improve Facebook's mobile monetization suggest these extensions of its business will also be monetized -- but it hasn't happened yet.

Facebook is vulnerable
While Facebook's stock has been on a near non-stop upward climb, it's possible the next genius in a dorm room has already invented its replacement. That may seem unfathomable, but the Facebook story would sound completely ridiculous if it weren't true.

So far, the social-media giant has turned back all contenders. (Remember the 10 minutes when Ello was relevant?) But the brief history of the Internet suggests that dominating social media can only last for so long, and Facebook is just as likely to fall victim to the trend as it is to buck it.

It may not be a question of if, but when. If the "when" comes after Facebook has established other platforms and products as major revenue sources, then perhaps the decline of the social-media site part of the company won't matter.

Until the company manages to make its diversification pay off, Facebook stock -- and perhaps its existence as a brand -- remains vulnerable.