By the time Facebook went public on May 18, 2012, the company had more than 900 million monthly active users, topped more than $1 billion in annual profits and even had an Oscar-winning film with Justin Timberlake cementing its place in popular culture.

But Wall Street, largely unimpressed with former members of NSync, was still wary of the social media giant's ability to keep it going.

Portfolio managers were "comparing it to MySpace and they were just worried," recalls Arvind Bhatia, an analyst who covers many of the big public Internet companies for Sterne Agee.

Today, according to Bhatia, the conversation among investors couldn't be more different. "It's completely the opposite of what it was: every portfolio you talk to says, 'Yeah, I get it. Facebook has to be a core holding.'"

On the third anniversary of a $16 billion IPO that many labeled as "disastrous" or worse, Facebook now consistently impresses investors with strong revenue growth, mind-blowing user numbers and a suite of applications and features with potential to bring in even more money as soon as the company flips the switch. Its stock, which fell to half the $38 IPO price after the first few months, is now trading above $80 a share.

More than that: Facebook now appears to be the lone public social Internet company that is standing tall.

Twitter, a rival social network that some investors hoped would be the next Facebook, has been pummeled repeatedly by Wall Street for disappointing user growth that throws into question its potential to ever be a mainstream service.

Last month, Twitter's stock fell more than 20% overnight after reporting worse-than-expected revenue, due in large part to what it characterized as "growing pains" with some of its advertising products.

Zynga, a gaming business whose Farmville rode Facebook's coattails, recently shuffled its top executives (again) and laid off 18% of its workforce (again) in an effort to cut costs. Yelp stock collapsed last month after missing earnings and revenue estimates — and the company is now said to be exploring a sale. Even LinkedIn — reliably at the center of the nation's professionals — recently got crushed after lowering its forecast for the year and admitting to a "drop in demand" for its ad products in certain markets.

And then there's Facebook — once written off, now standing far above its rivals.

FB data by YCharts

The new and improved Facebook

Investors had good reason to question Facebook's longterm potential in the lead-up to its IPO. Just days before Facebook went public, the company admitted in a regulatory filing that the fast user shift to smaller smartphone and tablet screens had started to cut into its ability to make money.

For much of its first year as a public company, it was judged mainly by that standard: would a social network created by college students for the desktop era be able to successfully run a $100 billion public company and manage the transition to the mobile era. The answer, as we know now, is an unequivocal "yes."

In its most recent earnings report, Facebook announced that revenue from smartphones and tablets now accounts for 73% of its total ad revenue. To put that another way: Facebook's mobile ad revenue has gone from effectively nothing at the time of its IPO to $2.4 billion just in the first quarter of this year.

Facebook accomplished that feat by re-thinking its applications from the ground up, introducing more and better targeting tools for advertisers and rolling out entirely new ad products like the tremendously successful app install ads, which have since been copied by competitors like Google and Twitter.

On top of that: Facebook's user base continues to grow and outmatch its competitors, helping its overall advertising pitch. Facebook has added roughly 500 million more monthly active users since going public. That's more than Twitter's entire 300 million monthly active user base.

Facebook in 2012 was primarily one big blue application. Now, it's a collection of applications that include the standalone Messenger (with more than 600 million users and payment features coming), Instagram (with an audience the size of Twitter and great potential for engaging advertisements) and WhatsApp (which may hit one billion active users faster than Facebook did). Facebook is also diving into video content, with the potential to one day rival YouTube in video ad revenue.

It recently began partnering with publishers to host articles directly on the social network, a feature that may bring in more revenue and keep readers on Facebook even longer — and has media experts wondering whether Facebook is going to eat the industry's lunch.

"It's the size of the network that makes them more powerful. They are truly global," says Bhatia, the analyst. "When you compare to Twitter's last quarter, despite all the success they’ve had, they told you they hit a wall on the direct response side because they didn’t have enough of a large network."

Bhatia credits Facebook's success to product innovations and a "more seasoned management team" that has learned from "having a rocky start" after going public.

Electronic screens inside the Nasdaq stock market announce the listing of Facebook shares before the start of trading, Friday, May 18, 2012 in New York. Image: Mark Lennihan/Associated Press

Bumps ahead

Even with all that success, Facebook is certainly not impenetrable.

While app install ads have helped Facebook build up a thriving mobile advertising business, it could be hit one day by a downturn in the tech or overall market, which might make it harder for many startups to pay for placement. Even in the short-term, Facebook faces competition from those who have introduced their own versions of that product.

There may not a mass exodus of teens from the social network, as some have long discussed. Instead, they may maintain accounts on Facebook, but choose to use the social network less, favoring more niche or ephemeral services like Snapchat and Yik Yak where their parents can't find them. That trendiness would ultimately make it harder for Facebook to monetize these users. Then again, Facebook has wisely acquired some of the properties they might flock to, like Instagram and WhatsApp.

Facebook is also susceptible to the same currency headwinds from abroad and European Union privacy and data collection crackdowns that have hit other companies like Google and Twitter.

How Facebook manages its challenges will influence not just the social media industry, but also technology, advertising, and publishing, as well as billions of global users. Everyone will be looking for something to like.