This week in social media, Twitter began its attempt to mainstream its user interface in earnest while finding out that 44 percent of "users" had never tweeted a word, Facebook's acquisition of WhatsApp became official, while all other messaging got consolidated into one app, and we found out that while Facebook isn't the biggest hit with teens, Facebook-owned Instagram is. It's time for Social Media Saturday!

Twitter

Twitter began rolling out its massive redesign of users' profile pages on the web. The new design has a super-wide cover photo at the top, the avatar picture on the left, and a large column of tweets, with lots of white space and a big display for pictures.

The new layout looks a lot like Facebook, which is a conscious move to try to make Twitter a little less intimidating to new users. This is further evidenced by the fact that while legacy users will get the new profile layout soon, the changes take effect immediately for any new users. Here's how it looks on our @LatinPostTech account:

Twitter also added a few new features, including "pinned tweets," which allows users to post their favorite tweet to the top of their profile page, and a feature that makes more-engaged tweets (tweets that have been retweeted, replied to, or favorited a lot) appear in a larger font, automatically.

Twitter began rolling out pop-up notifications to give users a heads up whenever they're mentioned, retweeted, or direct messaged.

These changes come at a time when Twitter is trying to lower its learning curve with new users and enhance user engagement, after going public on Wall Street and finding pressure to improve the numbers of active users.

And so the company couldn't have been very happy to learn that, according to TwopCharts, a web activity-monitoring site, 44 percent of Twitters almost 1 billion users have never tweeted anything at all. According to the Wall Street Journal, the report also showed that 30 percent of Twitter accounts have never sent more than 10 tweets.

Facebook

Facebook's incredible $19 billion acquisition of social messaging service WhatsApp was officially approved by the Federal Trade Commission this week. While allowing the purchase, the FTC warned that WhatsApp must continue honoring its pre-Facebook privacy policy.

"We want to make clear that, regardless of the acquisition, WhatsApp must continue to honor these promises to consumers. Further, if the acquisition is completed and WhatsApp fails to honor these promises, both companies could be in violation of Section 5 of the Federal Trade Commission (FTC) Act and, potentially, the FTC's order against Facebook," the letter states. That should alleviate some fears that WhatsApp die-hards had when Facebook acquired the company, though Facebook is literally a data company, so it's hard to imagine that the company won't try to leverage WhatsApp users' data in any way it legally can.

While the WhatsApp purchase is official, Facebook hinted this week that it would be keeping its Facebook Messenger app in the fold for a long time, by deciding to consolidate all Facebook messaging features into the app. Now, if you want to chat with friends on iOS or Android, you can't do it through the regular Facebook app -- the chat option now hotlinks to automatically open the standalone Messenger app.

Instagram

Facebook might not be cool anymore for teens, but CEO Mark Zuckerberg isn't worrying. According to a new (exhaustive) marketing study on teens by Piper Jaffray, Facebook-owned Instagram is the most important social network for teens now.

The study of about 7,500 teens of average age 16 found that 30 percent of teens thought Instagram was the most important social network, up from about 17 percent last year.

Facebook's importance for teens, according to the study, dropped precipitously from nearly 35 percent to just over 20 percent over a year, but taken together, they still beat Twitter, which has lost a little favor over the past 12 months.