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

Even social-media powerhouses aren't immune to common startup troubles. The latest: A New Jersey attorney is suing Pinterest and its early investor Brian Cohen, alleging that Cohen stole his concept for a similar social site and passed it along to Pinterest's co-founders. In his complaint, Theodore Schroeder says that he and Cohen were business partners in 2007 and 2008 when Schroeder developed a website, Rendezvoo, that was a precursor to Pinterest. Two of its elements -- content boards and so-called "infinite scrolling" -- are now key features of Pinterest.

Meanwhile, Pinterest reached another startup milestone this week by making its first acquisition -- recipe-sharing site Punchfork. Like Pinterest, Punchfork uses an image-based pinboard interface. The site will be closed and its personnel incorporated into Pinterest. -- AllThingsD and SocialTimes

Facebook adds voice messaging to mobile apps.
Running late to a meeting and need to tell your associate, but can't spare the typing time? Put away those tapping thumbs. Facebook has made it possible to record and send short voice messages through its Messenger app for iOS and Android. And the social-media giant is already testing a feature that allows free voice calls between Messenger users who are connected to Wi-Fi. -- PC World

Jakarta can teach us all about how to use Twitter.
If you aren't thinking globally when you're tweeting, you might be thinking too small. The U.S. has only 27 percent of the world's Twitter users. The city that ranks No. 1 for Twitter activity is Jakarta, Indonesia, according to data collected by Paris-based research firm Semiocast. São Paulo, Brazil is No. 4, ahead of New York. Never forget that anyone anywhere in the world can read your tweets, and that non-inclusive language -- calling the Fourth of July "our nation's birthday," for instance -- can turn off potential followers. -- AllTwitter

Facebook's fourth-quarter earnings report is coming soon.
Facebook announced that it will make public its fourth-quarter earnings in a conference call at 2:00 p.m. PST on January 30. The social network lost $372 million in the third fiscal quarter, and investors are no doubt eager to hear whether its recent experimentation with new advertising models has increased the health of its balance sheet. If so, it may inspire even more businesses to give Facebook's new ads a try, spurring growth for the company and opening up more marketing options for small businesses. -- AllFacebook

Social media can help you keep your New Year's resolutions.
Using social media for accountability and moral support can apparently help you keep your New Year's resolutions. How? Twitter and Facebook allow you to broadcast your goals to as many people as possible, how-to videos on YouTube can show you the way forward and blog sites such as Tumblr can be useful for keeping track of your progress. -- SocialTimes