THE $10 BILLION CLUB: Meet the most valuable startups in the US

Valuation: $10 billion

CEO Drew Houston

Dropbox reached its $10 billion valuation in 2014 after a $617 million funding round. Since then, the company has shifted its focus to business customers, launching Dropbox Enterprise in 2015.

The company began to cut back its lavish spending on employee perks in 2016, something that was costing the company $25,000 per year per employee. While Dropbox doesn't disclose its financials, it's reported to have generated more than $500 million in revenue last year. CEO Drew Houston said in 2016 that the company is free cash flow positive, which is a milestone for a fast-growth tech company.

News broke in July that Dropbox was working with Goldman Sachs on the paperwork for an initial public offering, but it's looking like the company won't file until at least next year.

Valuation: $12 billion

CEO Osman Kibar, CFO Cevdet Samikoglu, and chief medical officer Yusuf Yazici

San Diego-based Samumed is a health tech company focused on reversing aging. The startup has attracted $300 million in venture funding and a massive valuation, all thanks to a pipeline of what could be revolutionary treatments to regenerate hair, skin, bones, and joints.

Samumed was founded in 2008 and came out of stealth mode about two years ago when it started presenting some of its data. The startup is in the midst of several clinical trials and completed a 52-week Phase II clinical trial of an osteoarthritis treatment in July.

Valuation: $12.3 billion

CEO Ben Silbermann

In June 2017, Pinterest raised $150 million in funding from existing investors at a $12.3 billion valuation, bringing the app maker's valuation up slightly from $11 billion in April 2015.

The service, a combination of social network and online scrapbook, has more than 175 million monthly active users, over half of whom are international. The company has expanded its focus in recent months to overseas markets like the UK, France, Germany, Japan, and Brazil, and has doubled down on increasing the advertising on its platform. Last August, Pinterest acquired online bookmarking service Instapaper.

Pinterest reportedly expects to make $500 million in ad revenue this year, up 67% from $300 million in 2016.

Rumors swirled throughout 2016 that Pinterest was on the brink of going public, but its most recent influx of funding means an IPO could be delayed even further.

Valuation: $21 billion

WeWork cofounders Miguel McKelvey and Adam Neumann

Coworking startup WeWork has had a busy year. It raised $4.4 billion in funding from SoftBank Group and SoftBank Vision Fund over the course of several months; bought the Lord & Taylor Fifth Avenue building for $850 million to serve as its new headquarters; is adding a second headquarters at the new Salesforce Tower in San Francisco; led a $32 million funding round in New York startup The Wing; and has bought several other startups, most recently spending $200 million on Meetup.

WeWork is currently New York's highest-valued startup.

Valuation: $21.1 billion

CEO Elon Musk

SpaceX raised $350 million in new funding last July, putting its valuation over $21 billion.

The aerospace startup, founded by billionaire Elon Musk, has successfully pulled off 16 rocket launches in that last year, about double the amount from 2016. But SpaceX has also seen various setbacks along the way. In September 2016, a SpaceX rocket exploded during a launch-pad test, destroying a satellite Facebook intended to lease. More recently, the company's next generation rocket engine blew up during a test.

But the company is still pursuing an ambitious launch schedule, and Musk even plans to launch his Tesla Roadster into orbit in 2018. There's also growing speculation that SpaceX could even merge with Tesla somewhere down the line.

Valuation: $31 billion

CEO Brian Chesky

Home-rental startup Airbnb had a challenging 2016, but the company is still the second-most-valuable startup in the US.

Airbnb faced legal setbacks in San Francisco and New York last year, but also raised a massive, $850 million round of funding and launched a new service called Trips with the intent of becoming a more full-service travel company.

In March of 2017, Airbnb raised a $1 billion funding round that valued the company at $31 billion. In November, it acquired a startup called Accomable, which helps people with disabilities find accommodations on the road.

Now, Airbnb is reportedly keeping a close eye on Spotify's rumoured route to going public through a direct listing — if it goes well, we may see a publicly traded Airbnb stock next year.

Valuation: $68 billion

CEO Dara Khosrowshahi

Despite a year of upheaval, scandal, and legal challenges, Uber is still the most valuable startup in the US.

The ride-hailing startup raised several billion dollars in recent years, including $3.5 billion from a Saudi Arabian investment fund and $2 billion in the form of a leveraged loan. Most recently, Bloomberg reported that Japan's SoftBank plans to buy stock in Uber from existing shareholders at a $48 billion valuation, a steep discount to the ride-hailing company's current valuation.

Finances aside, Uber will likely be glad to see 2017 come to a close. The startup has been accused of gender discrimination and sexual harassment, is involved in an acrimonious lawsuit with self-driving car firm Waymo, and has had to replace CEO Travis Kalanick, who stepped down amid the scandals and the sudden death of his mother. Dara Khosrowshahi was named CEO in August.

Uber has committed to going public by 2019.