StumbleUpon recently reported that it has surpassed 20 million users since launching in 2002.

Website discovery tool StumbleUpon now has 20 million users, the company announced in its blog last week. According to CEO Garrett Camp, StumbleUpon has developed the majority of its user base in the last year alone.

Initially launching in 2002 as an add-on in Mozilla Firefox, StumbleUpon now receives more traffic in an hour than it did in its entire first year.

For marketers, creating compelling marketing content can help it appear in StumbleUpon and possibly convert prospects they may not have reached otherwise. StumbleUpon presents users with content based on a predetermined list of interests. The social element of the service is critical to its utility. Web pages shared frequently on social platforms are more likely to appear to StumbleUpon users.

While StumbleUpon is less popular most other social sites on the web, the unique service can provide a strong understanding of how interesting and valuable users consider a website.

Brafton reported earlier this year that StumbleUpon registered more social referrals than channel leader Facebook. Numbers from 2010 indicated that StumbleUpon claimed 43 percent of referrals compared to 38 percent for Facebook, which means marketers shouldn’t estimate of having their content Stumbled.

Joe Meloni is Brafton's former Executive News and Content Writer. He studied journalism at the University of Massachusetts, Amherst, and has written for a number of print and web-based publications.