Facebook Groups is an excellent source for finding virtual communities about topics such as parenting tips, local restaurants, and pet care. The world's biggest social network is testing a "Discover" feature in the Groups section that makes it easier for Facebook users to join conversations. It will be available for iOS and Android devices in the United States.  

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A new "More" tab lets users browse public and closed Facebook Groups including those that friends are in, and local Groups, according to Mashable. They can use their smartphones and tablets to see trending topics in their circle of friends, and in their city or town.

The new feature is reportedly easy to use. It is also similar to the discovery tools on Twitter and Instagram. However, it is also surprising that the social giant did roll out the feature a long time ago.

Discover includes 25 categories. They include buy & sell, networking, travel, hobby & leisure, support & comfort, sports, food, sports, and animals & pets. Every topic page highlights the Groups with the most suggestions. They are based on popularity and group members people might know.    

Group admins can decide whether or not their Group will appear in the Discover tool, according to Fast Company.

In the past it was more difficult to find Groups. Facebook users had to type keywords into the social network's search bar, or wait until a friend sent them an invitation to join.

A limited number of people have access to the Discover feature now, but it will get a broad roll-out in the near future.

Groups is the most used feature in the Facebook app after News Feed. Each month around one billion people use Groups.

Meanwhile, there are also tens of millions of active Facebook Groups. The average Groups user has joined around 12 Groups.   

One example is Iceland's "Good Sister" Facebook Group. Over one-quarter of the country's population has joined the group that celebrates other Icelanders.

However, the social network has also taken steps to shut down certain Groups. They include those that promote illegal activities.

In related news, a California District Judge ruled that Illinois Facebook users can continue with their class-action lawsuit. It argues the website's feature breaks a 2008 law by using facial recognition software for photo-tagging.

Here's how to find large Facebook Groups: