Facebook vs. Twitter: Here's how they're different

It's natural to mention Twitter and Facebook in the same breath, but they are very different companies. Yes, of course Facebook's built on the idea of connecting friends, while Twitter is designed for people from all over the world who haven't met to carry on a global conversation.

But Twitter's initial public offering filing revealed just how unlike these two companies really are.

(Read more: No more secrets: Twitter IPO filing is now public)

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First, Twitter is a much smaller company, with 215 million monthly active users, compared with Facebook's 1.15 billion. Last year when Facebook filed to go public it had 845 million.

At the time of its IPO filing, Facebook was profitable, and had been for three years—Twitter still isn't profitable. It made progress toward profitability in 2013, with net losses decreasing 38 percent to $79.4 million. But, in the first half of this year, thanks to a slew of acquisitions, its net losses increased 41 percent to $69.3 million.

Why the discrepancy? Twitter didn't include any ads for years—it launched its first ads, "promoted tweets," in the summer of 2010, but didn't launch any ads on mobile until last summer. Facebook, in contrast had some sort of ads when it launched back in 2004, and opened up to ad networks in 2006.

And while Facebook spent 7.5 percent of its revenue on "general and administrative costs" in 2011, the year before it filed, in 2012, Twitter spent 18.8 percent of its revenue. Before its IPO Facebook spent 11.5 percent of its revenue on sales and marketing, Twitter spent 27.3 percent.

(Read more: Twitter lights up Twitter with Twitter IPO)

To Twitter's credit, its revenue is growing very fast, faster than Facebook's. In 2012 Twitter's revenue tripled to $317 million, and in the first half of 2013 Twitter's revenue more than doubled to $254 million.

Also, Twitter has strength in mobile, which is in sharp contrast to Facebook when it went public. Three quarters of Twitter's users access the service through a mobile device, accounting for 65 percent of ad revenue.

At Facebook's IPO it had zero mobile revenue, posing a major challenge—detailed in its S-1 filing under "Risk Factors." Now Facebook has grown mobile to over 40 percent of its mobile revenue; for both companies this is still a major area of growth.

Even Twitter and Facebook's ownership structures are different. Twitter has no controlling shareholder with special voting rights: The largest stakeholder is co-founder and former CEO Evan Williams with a 12 percent stake, while Chairman Jack Dorsey has 4.9 percent.

(Read more: Twitter's entire S-1 filing)

It only has a single class of shares, while Facebook is a totally different story. It qualifies as a "controlled company" with a huge amount of power lying in the hands of CEO Mark Zuckerberg, thanks to his 57 percent ownership of Facebook's Class B voting shares.

We'll see whether giving each shareholder the same vote—just like each Twitter user has the same voice—ends up helping Twitter, or whether the fact that Facebook's controlled by Zuckerberg's controlling vision gives it the advantage.

—By CNBC's Julia Boorstin. Follow her on Twitter: @JBoorstin.