This week's need-to-know social-media news.

Among the takeaways from Facebook's fourth-quarter earnings report this week was this: Mobile advertising is a serious revenue driver. The social network's revenue grew 40 percent in the fourth quarter of 2012 compared to the same period the previous year, beating analyst expectations. Of that, mobile ads accounted for 23 percent of ad revenue, up from 14 percent in the previous quarter.

The growth of mobile -- more Facebook users now visit the site through mobile apps than a desktop computer -- is good news for Facebook and for advertisers, who have long hoped the platform could deliver results commensurate with its enormous user base. Co-founder Mark Zuckerberg predicted that Facebook would eventually make more money on every minute of Facebook mobile traffic than on desktop traffic. -- The New York Times

Foursquare launches a new app for businesses.
This week, Foursquare released a standalone app for business owners. A mobile extension of its desktop merchant tools, the app allows businesses to see recent check-ins, update specials and post promotions to social networks while on the go. Major retailers can't use the app, according to AllThingsD, but it should allow small businesses to engage more conveniently with customers. -- AllThingsD

Dropbox updates with new social features.
Popular cloud computing service Dropbox announced that over the next month it will release new features designed to make its service more social and content-oriented. Known for secure data backup, Dropbox is now separating some types of content, such as photos and songs, from file folders, and making it easier to share them. Say you have a folder of pictures of your employees during company-wide event or interacting with customers. Now you'll be able to select which ones you want to share and easily share them -- via Facebook, Twitter or email -- in a virtual album. -- AllThingsD and Wired

Super Bowl advertisers see results with pre-game YouTube spots.
With social media's ability to spread advertisements virally, more Super Bowl advertisers are releasing their game-day commercials early by posting them to YouTube. It seems a smart strategy: Commercials or teasers posted online before football's big game received an average of 9.1 million YouTube views last year. Those posted after airing on TV averaged only 1.3 million views. "Money that we might not have invested in [digital and YouTube] around the Super Bowl, we are investing it now," said Lucas Herscovici, vice president of digital for Anheuser-Busch. -- Fortune

British company burned when employee live-tweets layoffs.
Sometimes, allowing employees access to your social media accounts can backfire. That's what happened to U.K.-based electronics company HMV this week when one or more soon-to-be former employees took to HMV's official Twitter account to live-tweet details of company-wide layoffs. The first tweet read, "We're tweeting live from HR where we're all being fired! Exciting!! #hmvXFactorFiring." This update came a little later: "Just overheard our Marketing Director (he's staying, folks) ask 'How do I shut down Twitter?' #hmvXFactorFiring." The company eventually regained control of its feed and deleted the offending tweets -- but not before an editor at The Guardian newspaper captured them in a screen grab and, appropriately, tweeted it. -- PRDaily