It’s hard to tell if Tumblr is a social network or a blogging platform, because the thing is, it’s both.

As a blogging platform, it offers an easy way to quickly share text or multimedia content. But Tumblr also has a social component. There’s a newsfeed, which, similar to Twitter or Facebook, updates as the people you follow publish posts. And like Facebook and Twitter, the quality of the content depends on whom you follow.

Tumblr is like a long-form Twitter. It’s also similar to Facebook, if instead of following your friends from middle school, you followed news organizations and content creators.

Launched a little over five years ago, Tumblr now boasts nearly 60 million blogs with nearly 25 billion posts. And it’s growing. The site receives 25,000 new users and 40 million new posts each day. The service is most popular with the teen and college-aged user segments with half of Tumblr's visitor base being under the age of 25.

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In other words, if your brand isn’t already on Tumblr, you probably should reconsider that position.

At PR Newswire, we use Tumblr in a few ways, among them:

• To recap the various conferences our team attends throughout the year;
• To share relevant social media and publishing news found on other Tumblr blogs (we do this by reblogging);
• To post news releases about topics such as the Muppets, cupcakes, or the energy drink Four Loko.

We joined Tumblr for the same reason all brands do—that’s where people are. The number of users on Tumblr is impressive. But its growth rate is truly exceptional.

Other media such as The Atlantic, The Economist and The Los Angeles Times have helped reestablish their brands by embracing this new digital space and consistently publishing relevant and interesting content. The Economist, for example, teases pictures and graphs to upcoming print issues.

Fashion bloggers have thrived in this space as well. Retailers like Urban Outfitters use it to promote new styles, while smaller blogs like Put This On taps Tumblr to promote suggested outfits and eBay sales. It’s no surprise that the more successful (or “viral”) Tumblr posts are those with photos.

To that end, the food industry also has seen some success with Tumblr. For example, Boqueria Restaurant of New York not only shows the final product, but also behind-the-scenes glimpses into its kitchens. Lost Weekend coffee shop on New York’s Lower East Side publishes artful portraits of its drip coffees, along with pictures of the fashionable clothes for sale at the shop and other images, videos, and mp3s it thinks their audience (and customers) will find interesting.

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What’s particularly appealing about Tumblr from user’s perspective is that you can see all of this—and lots more—in one streaming newsfeed.

A signature aspect of Tumblr is its absence of advertising. Depending on your point of view, this is either a good or bad thing. For years, Tumblr resisted the idea of selling space to advertisers. Recently, however, it began to change its tune. Maybe it saw an opportunity. Perhaps it wanted to appease investors. One thing it's not planning to do is to go the route of traditional advertising.

“The overall thesis of what we’re trying to do is empower and highlight interesting creative advertising,” said Derek Gottfrid, Tumblr’s vice president of product.

What this means is that an opportunity now exists for brands to tell their stories to Tumblr’s vast, growing audiences. This probably doesn’t mean pop-up or tacky banner ads. But it does mean that a window is opening to a vast audience of potential customers.

Thomas Hynes is manager of blogger relations at PR Newswire. Find him on Twitter @ThomasHynes.

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