1. Tencent
For building a suite of communications apps that 300 million Chinese are talking through. That massive audience has flocked to Tencent’s WeChat (or Weixin, as it’s known in China), the Chinese Internet giant’s suite of social networking plug-ins, in less than two years. Why? WeChat is less expensive, clearer, and faster than calling people on the phone.  In America, WeChat is a top 20 free social networking app in Apple’s App Store.

2. Pinterest
For unlocking our image obsession. A year ago, the social scrapbooking site was dubbed the fastest-growing web service in history. Where do you go from there? Up. Pinterest is now one of the top 50 most-visited sites in the U.S., and retailers are excited. The average purchase off a pinboard nets more than double those off a wall post or a tweet.

3. Buzzfeed
For reinventing how news (and advertising) is shared. When he founded BuzzFeed in 2006, serial entrepreneur Jonah Peretti–who’d previously cofounded the Huffington Post–thought of it as a new-media mad-science lab. Social sharing was the next big distribution channel, he reasoned, and BuzzFeed was a place to create silly shareable content. The site is still brimming with listicles and cat videos, but over the past year, BuzzFeed has undergone a remarkable transformation: It’s now also a serious news site and a pioneer in the world of social advertising.

4. ModCloth
For letting its community help fill the racks. Customer engagement proves profitable for Susan Gregg Koger and her husband Eric, founders of the virtual thrift shop turned e-commerce success story. Through its Be The Buyer program, products brought to market through customer voting sell twice as much. ModCloth took that to the next level in 2012 by letting the community actually submit designs too. Visit any of their social platforms, from Facebook to Twitter, and you’ll see creative interactive campaigns and a commitment to user engagement.

5. Science
For creating a socially-savvy e-commerce startup factory. The name is not an accident. For CEO Michael Jones and his partners, launching disruptive e-commerce companies means deep analysis of big bets. They also specialize in identifying the best social tools to create fans and turn them into customers and brand advocates. For example, Heather Lipner’s Uncovet harnesses social data to make a virtual, personalized boutique for each of her 200,000-plus subscribers; Hello Insights helps companies use a data-driven approach to turn Pinterest users into shoppers; Dollar Shave Club’s Michael Dubin created the viral marketing video of the year for his subscription shaving gear.

6. Fab
For evolving into the social commerce destination for design wares. Visit Fab’s website, and you find something akin to a social network for the design-obsessed. In fact, Fab started off as a social network, so you could say social media is baked into its DNA.

7. Tumblr
For proving that ads and great content can mix in social media. Last May, the image-heavy, meme-tastic social network entered the fraught world of social media advertising–but demanded that brands act like its users. That meant creating visual, beautiful, fun, shareable content. The response was impressive: By year’s end, Tumblr had vaulted into the top 10 most-visited websites in America, with more than 80 million blogs that net more than 700 million visits and almost 18 billion page views.

8. AngelList
For being the Match.com for startups. Venture capital was a who-you-know business, until AngelList made a mass introduction. Like online dating, its transparent network connects startups with accredited investors, and now even well-connected entrepreneurs are using it. Success stories include Uber, BranchOut, and GetAround–and its recent partnership with the private exchange SecondMarket lets any accredited investor put as little as $1,000 into a startup.

9. Github
For speeding up the pace of software development. It’s not just a social platform, it’s a collaborative platform: Like a coder’s wiki, it allows programmers to co-develop and share code. Facebook used it to build a bug-tracking tool; LinkedIn uses it to maintain its People You May Know and Skills & Endorsement features. GitHub also offers custom services for corporations, to let businesses collaborate on code internally.

10. Branch
For reimagining what conversation looks like online. Branch is a place where Twitter conversations go to live better. Where Twitter is an egalitarian free-for-all–anyone can butt in, uninvited, to any public conversation on Twitter, for better or worse–Branch fosters highly-curated conversation. Hosting a Branch is like holding a dinner party or a salon in a glass living room: anyone can watch, but only the chosen can participate. Unlike most other social networks, Branch isn’t cloistered away inside its own domain or apps: Branch conversations can be embedded on other websites; chaotic Twitter conversations can be “Branched” into more serene Branch threads; and individual Branch comments can be Branched into separate conversations, as well.

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