Who are you missing by not recruiting via social networks?

College students who spend hours a day on Facebook might not be wasting their time, several studies suggest — they might even find jobs through social networking.

That’s because savvy employers, according to new report, are increasingly recruiting through social sites like Facebook, LinkedIn, Twitter and others.

The report, published in the Daily Pennsylvanian —  the student newspaper of the University of Pennsylvania’s Wharton School — cites one study that predicts the number of recruiters using Twitter alone will quadruple this year.

Meantime, applicants are doing the same. LinkedIn reports that students and recent college graduates are the site’s fastest-growing user demographic.

The Daily Pennsylvanian article quotes Shannon Kelly, an associate director of Wharton’s Career Services program, who notes that social networking sites give employers immediate and personal access to job-seekers.

And that can give companies a leg up on their competitors.

“More and more companies are using social media platforms to showcase business culture … it’s no different from hiring a public relations company,” Kelly tells the paper.

Wharton junior Jacob Schulman wound up with two unsolicited job offers via Twitter.

“I wasn’t proactively searching for jobs,” he says in the Daily Pennsylvanian article. “I was just following companies that I liked.”

Seems like a serendipitous outcome — Schulman gets an offer from a company he’s genuinely interested in, and the company has a candidate who’s already proven he’s serious.