This week in social media, Facebook faced increased scrutiny in Europe while subsidiary WhatsApp finally launched its calling feature on Android. Meanwhile, Twitter's Periscope dominated Meerkat right out of the gate and Pinterest reached its fifth anniversary stronger than ever.

It's time for Social Media Sunday!

Facebook:

Privacy Policies Face Increased Scrutiny in Europe

European regulators have increasingly clamped down on American tech giants like Google, Apple, and Amazon -- you may remember Europe's opening "right to be forgotten" saga from last year -- and Facebook isn't exempt from the EU's regulatory scrutiny either.

Regulators from France, Spain and Italy recently joined a European regulatory group examining how Facebook collects and uses personal data, according to a Wall Street Journal report. The addition of those regulators doubles the number of European countries probing big blue's data practices, as they join Dutch, German, and Belgian authorities already investigating the world's largest social network.

European officials are seeking to determine details on Facebook's advertising policies, like how the company combines user data from subsidiaries like Instagram and WhatsApp to target ads and how Facebook's "Like" button tracks user Internet browsing.

Up until recently, Facebook was effectively exempt from broader European inquiry and regulation, as regulatory responsibility over the giant company was originally assigned only to Ireland, where Facebook's European headquarters is based. Now, as broader European investigations ramp up, Facebook could eventually be forced to change its data practices or pay millions of euros worth of fines.

Riff: Facebook's Latest Snapchat-like App

Mark Zuckerberg still must be feeling the burn from Snapchat's "no thanks" to his billion-dollar buyout offer, because Facebook is still challenging the king unicorn social media startup with new apps.

This time it's Riff, a new video app that seeks to challenge Snapchat's "Our Stories" sharing feature, and possibly to pick up on some of that Meerkat and Periscope-fueled social video buzz.

Riff encourages users to create chains of short video clips under one hashtag, resulting in a kind of collaborative, collective viral video that already has a social media-sharable hashtag built-in from the start.

Or so Facebook hopes. Judging by Facebook's announcement language -- describing Riff as a "side project" put together "after-hours" on a "hunch" -- Facebook is just as skeptical of Riff's potential to take off. Nevertheless, it sounds intriguing, and you can get it for Android or iOS now.

WhatsApp: Calling Feature Finally Debuts

The long-awaited VoIP (data-) calling feature for WhatsApp has finally hit in the form of an updated Android version of the app. Except, you can't get it from the Google Play store right now.

Instead, you can download the Android APK file directly from the WhatsApp website here (version 2.12.5) and sideload it onto your Android device (if you know how to do that kind of thing). A calling-enabled version of the iOS app has not been released yet.

Twitter:

Periscope Wasn't First, But Now It's More Popular

Last week, we wondered why Twitter would focus so much energy on hobbling third-party video streaming app and SxSW favorite Meerkat to give its rival subsidiary Periscope an edge, even though Meerkat's breakout popularity last month was reviving the relevance of Twitter as a social network in general.

Now it's time for me to eat crow: Turns out Twitter was right on this one, because Periscope is pretty much destroying Meerkat just one week into its public launch, according to MarketWatch. While Meerkat reached 140 in top U.S. iOS app downloads at its peak, Periscope hit 31 on the iOS charts within 24 hours of its launch.

It remains to be seen which rival wins in the end, and Periscope is already losing some of its fresh-app luster and buzz, but so far, it's become clear that Twitter has a pretty strong hand, even if late in the game.

TenXer Acquisition

Speaking of acquisitions, Twitter reportedly bought, closed, and consumed tenXer this week.

TenXer is a company that focuses on data engineering management, development, and other technical aspects, and according to TechCrunch, Twitter is shutting down the company adding the whole team to its workforce. Hopefully it means my Twitter app eventually won't crash as regularly as it does now.

Pinterest:

Five Years Old, with a Bright Future

Pinterest turned five this week, and according to a USA Today interview with the company's cofounder Evan Sharp, the sky's the limit on its future.

The private startup reportedly raised $367 million this year, with plans to use more than half a billion to expand Pinterest's team internally, with an eye on developing more mobile and even smartwatch features in the future.

"We feel good about the next five years," told Sharp to USA Today. With its recent year-to-year growth of unique visitors almost at 50 percent in February, that's not surprising.

Follow Robert Schoon on Twitter.