StumbleUpon: 20 Million Stumblers & Counting

Social search and discovery site StumbleUpon has announced a new milestone: The site recently surpassed 20 million users.

The company’s announcement is filled with some interesting stats that show its growth since launching as a Firefox add-on back in 2002:

• StumbleUpon now serves as many “stumbles” in one hour as it did during its first year.
• At peak activity, there are more than 1,000 stumbles per second.
• The user base has doubled from 10 million members in May 2010 to today’s announcement of 20 million members.

There’s also a chart showing many of the site’s milestones over the past nine years.

(click for larger version)

Often overlooked in the search/social marketing industries where Facebook and Twitter tend to dominate the conversation, StumbleUpon has remained active with new features in the last 12 months such as the “Explore” search box and an expanded ad platform.