There's no denying the outstanding long-term results Amazon (NASDAQ:AMZN) shareholders have enjoyed over the years. Finding stocks that could not only match, but even outperform the online king is a tall order, but we found three hearty souls willing to take on the challenge. The three stocks include beleaguered Twitter (NYSE:TWTR), along with Inovio Pharmaceuticals (NASDAQ:INO), and that "other" social media site, Facebook (NASDAQ:FB).

Picture of several gold coins stacked neatly.

Image source: Getty Images.

This is not going to be a popular pick

Rich Smith (Twitter): Amazon.com made headlines last week when its stock price broke above $1,000 a share. At that price, Amazon stock achieved the even more impressive statistic of having risen more than 5,000 times in value since its IPO 20 years ago.

Those are some pretty amazing statistics -- but here's something even more amazing: For the first five years of that 20-year run, Amazon didn't earn any profit at all. Zero. Zilch. In fact, the company's profit margins ran negative all the way through 2002. (Although in 2002, Amazon did generate positive free cash flow of $135 million).

All of this suggests that if we're looking for a company that could put Amazon's returns to shame, we may need to throw out the rulebook and not look for companies that earn strong profit margins -- or even any profits at all as GAAP calculates such things -- today. What we may want to look for instead are companies that are growing revenues at mind-numbingly fast rates (Amazon, for example, grew its revenues more than 25 times between 1997 and 2002), or at a rate of roughly 190% annualized) and are generating strong positive free cash flow at the same time.

Does any of that sound familiar to you? Because to me, it does. To me, it sounds a little bit like Twitter.

Loathed by investors who point (and shake their fingers at) Twitter's failure to ever earn GAAP profits, Twitter has nonetheless managed to grow its sales at about 88% annually over the past five years. For most of its time as a public company, Twitter burned cash while growing sales. But two years ago, Twitter finally turned free-cash-flow positive, and over the past 12 months, Twitter has generated positive free cash flow of more than $600 million.

Granted, few analysts see much hope for Twitter continuing this run. Twitter's sales stalled last quarter, and consensus estimates say the company won't grow earnings at more than 9% annually over the next five years. But if Twitter can regain its growth path and keep the cash flowing, I think this stock has at least the potential to put Amazon's returns to shame.

And to think it's just getting started

Tim Brugger (Facebook): As my associate Rich notes, Amazon is a fairly unique stock in terms of how it's evaluated, but there's no denying its sky-high returns. It may come as a surprise, but Facebook has handily outperformed Amazon the past five years -- 467% to 357% -- and that's not likely to change.

Granted, Facebook has only been publicly traded for five years, so it doesn't boast a long track record, but it's unique among relatively new stocks. Better still, several signs point to Facebook continuing its incredible run regardless of its already enormous size and reach.

There was a time not long ago when pundits voiced concerns of "market saturation," particularly since only half of the world's 7.5 billion population are "connected." Not to worry. As of last quarter, 52% of the 3.7 billion global internet users access Facebook every month, and an even more impressive 34% of the world's connected population visit their "friends" every day.

Facebook still has half of the online world to bring on board, and with the advent of lower-cost smartphones hitting emerging markets, the total prospective customer base should keep growing. And despite its size, Facebook continues to deliver hyper-growth-like results.

Facebook's total revenue climbed 49% to $8 billion in the first quarter, which is the kind of performance shareholders have come to expect. Now with Instagram monetized and still growing, and the billion plus monthly users of WhatsApp and Messenger waiting to boost revenue still higher in the years ahead, Facebook's upside is nearly limitless.

This speculative biotech has sky-high growth potential

George Budwell (Inovio Pharmaceuticals): If you're hunting for stocks with a realistic shot at replicating Amazon's mind-boggling growth curve, you're probably gonna need to mine the depths of the speculative biotech space. As a prime example, the DNA-based vaccine maker Inovio Pharmaceuticals is a name that has some truly staggering growth potential based on its current clinical line-up -- but it also comes with a hefty dose of risk that may unnerve more conservative investors.

Inovio's value proposition hinges on the success -- or failure -- of its DNA-based vaccine platform to provide novel treatment options for patients with cancer or infectious diseases like HIV. While these next-generation vaccines offer an unusually rapid development timeline and a potentially unprecedented ability to fight emerging infectious diseases in a timely manner, they have also struggled to produce high enough efficacy levels to warrant a regulatory approval for human subjects -- at least so far.

Inovio believes its Cellectra 5PSP delivery device and the addition of immune-boosting agents can solve this lingering problem -- paving the wave for a flurry of DNA-based vaccines in the coming decades.

The first real test of the company's proposition is its late-stage candidate VGX-3100 that's initially targeting women with cervical dysplasia caused by the human papillomavirus. The main drawback with this stock is that VGX-3100 is, at a minimum, two years away from producing a top-line readout that might lead to a regulatory approval. In the meantime, the company is probably going to rely on the public markets for financing to a large degree. If Inovio strikes gold with VGX-3100 and validates its platform, though, this stock could produce some awe-inspiring gains for early investors.

George Budwell has no position in any stocks mentioned. Rich Smith has no position in any stocks mentioned. Tim Brugger has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Amazon, Facebook, and Twitter. The Motley Fool has a disclosure policy.