How These 10 Marketing Campaigns Became Viral HitsAny company can create word-of-mouth ad -- all it takes is a clever idea and skillful execution.

Getting your brand noticed viasocial mediagrows more difficult with each passing day. Users upload 100 hours of video to YouTube every 60 seconds and share more than 4.75 billion pieces of content on Facebook every 24 hours. Add to that 500 million new tweets per day, and the chances of breaking through to a wider audience can seem virtually nonexistent.

But smart, savvy companies of all sizes are still exploding into the mainstream consciousness by creating campaigns that compel consumers to share content with their social graphs. Some campaigns are hilarious; others are heartbreaking. But all contain triggers that get people talking, says Jonah Berger, marketing professor at the Wharton School at the University of Pennsylvania and author of the bestsellerContagious: Why Things Catch On.

"Emotion is one factor that drives sharing. We see lots of funny stuff go viral on YouTube, but we also see angry political rants get shared," Berger says. "Any emotion that fires us up--humor, awe and excitement, but also anger and anxiety--drives us to share."