StumbleUpon is a discovery engine meant to search for the best recommendations of web content for you. Users of StumbleUpon give a site a thumbs up or a thumbs down when bookmarking it to their StumbleUpon homepage. Social media marketers can advertise their business to drive more traffic to their website. The purpose of advertising on StumbleUpon is to get their users to recommend their site which in turn brings more users to see and recommend as well. It is also helpful to recommend content that is related to their niche and target audience so their audience and their friends will follow them too. But keep in mind not to spam users. StumbleUpon has millions of users registered with them. As explained in ClickOpp, over 1 billion stumbles are added per month. In addition, StumbleUpon bookkmarklet is available on all major browsers and mobile devices such as iPhones and Android phones.