-By Mike Shields

When Meebo launched five years ago, the plan was to create a Web destination where users could aggregate all of their instant messaging communications in one place.

But over the past year, the company has rolled out an increasingly popular toolbar for publishers wishing to socialize their sites. Since last August, its user base has ballooned by 300 percent to 54.4 million unique users in May, per comScore. And that figure is sure to swell, as Meebo has recently added EW.com and Seventeen and will soon add TVGuide.com to its group of 4,000-plus publishing partners.

The Meebo toolbar sits at the bottom of a publisher’s site. It’s designed to make it easy for users to share content since they can simply drag and drop links and automatically share them with friends via whatever social platform they use, including Facebook, AIM and Twitter.

Publishers say the toolbar increases user engagement and ultimately delivers more traffic. According to Cyndi Stivers, EW.com’s managing editor, since implementing the toolbar in April, users have shared stories 60,000 times, resulting in 100,000 clicks back to the site over a three-month period. “We want to make it as easy for our audience to share articles whenever they feel like it,” Stivers said. “And the traffic back is key.”

EW.com has also enjoyed an ad revenue boost. Recently, the hit kids movie Despicable Me ran ads on the toolbar on EW.com and other sites (with Meebo sharing a portion of the revenue). Doug Neil, svp of digital marketing for Universal Pictures, said the campaign delivered great engagement. “Ads really stand out on their platform, and they add a social element,” Neil said.

Meebo is set to introduce two new toolbar placements aimed at taking its ad business to another level: a “Sponsored Button” that will appear persistently on the toolbar, as well as a much more in-your-face “Borderless Execution”—a homepage takeover ad that is triggered when users mouse over it.

“The Sponsored Button is really for advertisers that want to push out their own content,” said Carter Brokaw, Meebo’s chief revenue officer. “The Borderless unit is about unleashing brand advertisers’ creativity.”