Are you reading this story on your phone via a link on Twitter, Facebook or some other social network? You’re not alone.

A new study by research firm comScore says 64.2 million U.S. citizens use their mobile devices for social networking, with more than half of them doing so “almost every day.”

A full 38.2 million people use social networks on their phones or tablets on a “near daily” basis, according to the report. What exactly are they doing? Reading updates from friends, the study says, with 84.6% of mobile social networkers checking out “posts from people known personally.” Posting status updates was the second most popular activity, with 73.6% of users partaking. It’s important to note comScore counts reading blogs as social networking.

While the study found users are most likely to read posts from friends, it also says people are increasingly using their social networks to interact with brands and organizations. Almost 58% of U.S. users read posts from companies or brands, and about 32% are said to be likely to click on ads while social networking.

The overall number of people experiencing social networks through their phones or tablets is surging. That 64 million figure is up 77% from the year before, and daily users are up 88%. That growth is tied directly to smartphone adoption, which comScore says is up to 41.8% of the phone-owning audience — up from 27% just a year ago.

The top app that people use to get their social on is Facebook. On both iOS (iPhone, iPad and iPod Touch) as well as Android, Facebook is the top social-networking app on mobile. Twitter is a distant second, much lower in the ranks than Facebook and even placing behind the social game Words With Friends on both platforms. (The list of top apps on iOS and Android is below.)

Although mobile social networking is rising rapidly, it’s not the reason people buy a smartphone. The study says a particular phone’s social-networking abilities was far down the list of factors in a purchase decision, the No. 1 being the network quality of the mobile service provider. The phone’s operating system and overall app selection also rank highly.

How often do you get social on your smartphone or tablet? Do you think the comScore study accurately reflects how people use social media on mobile devices?