Everybody talks about using Facebook and Pinterest to build referral traffic—but what about StumbleUpon? In 2011, Forbes published findings that StumbleUpon had surpassed even Facebook as a source of social media traffic in the United States. While statistics change over time, one thing is certain: StumbleUpon is not a bookmarking site to overlook. So what do you need to know about this tool? How can using StumbleUpon build traffic on your website? Here are three steps and a few general guidelines to make the most of this network…