Updated: Stumbleupon — Not Much Attention, but Big Traffic

Updated: As a number of readers have pointed out, I read this chart incorrectly. I read absolute numbers of visitors into it, whereas the chart is actually meant to show percentages of traffic. I’ve tried to correct my mis-impressions below — although the chart does still show that Stumbleupon drives a lot of traffic, so my conclusions are not completely wrong.

In a chart of the traffic it gets from a variety of social networks (posted by All Things Digital), Gawker Media showed that the number one referrer is Reddit — which has been gaining momentum recently, thanks in part to the reaction to Digg’s relaunch, but was number one as far back as last year Facebook. Some observers used the chart to point out how much Digg has fallen off in terms of its influence, while others used it to show how Twitter is not as mainstream as most people think. What struck me, however, was how little attention gets paid to the number two and three of the leading referrers on that graph: namely Fark and Stumbleupon.

According to my reading of the chart, Fark drove more than 18 million visitors to Gawker in August — up from less than 10 million in the same period last year — while Stumbleupon drove about 16 million, about double what it sent the network of websites in the same month a year earlier. Twitter accounted for around 12 million (which was still twice the number of visitors it drove a year ago) and Digg was responsible for just under 10 million of the site’s 20 million total visitors in August. Facebook is still in last place, according to Gawker’s numbers, but it’s been growing sharply.

The chart shows that the largest proportion of Gawker’s 20 million total visitors in August came from Facebook, which has gone from being an also-ran to the overall leader in the past year. The proportion of traffic that comes from Digg has shrunk over that period, but the traffic coming from Stumbleupon has grown substantially, putting it a close second place (judging by the size of the colored bars representing each site). Reddit’s share of traffic has also grown, as has Twitter’s.

Fark, which was founded by Drew Curtis in 1999 as a way to share funny links with his friends, doesn’t get a lot of press attention. In fact, the service is virtually never mentioned in stories about Digg’s redesign or the rivalry between Digg and Reddit, or even in stories about Twitter and its growth as a traffic driver. Yet it and Stumbleupon drive relatively huge numbers of readers to many websites. Fark reportedly has more than four million unique visitors a month. Is the lack of attention because Curtis keeps a low profile (he still lives in his home town of Lexington, Ky.), or because the site isn’t venture-funded and isn’t located in Silicon Valley? It’s anyone’s guess.

Meanwhile, Stumbleupon — which was started by Canadian Garrett Camp and a small group of friends in 2001 as a spinoff from Camp’s graduate-school research project in Calgary, Alberta — gets a little more press because it was backed by VCs and ultimately bought by eBay (s ebay) in 2007 for $75 million. While there was some attention paid to the company after it was bought back by the founders and a small group of venture investors in 2009, the newly independent startup has kept a pretty low profile since. Despite the lack of headlines, however, many publishers (including GigaOM) know that when a link gets “stumbled,” there can often be a huge influx of readers.

Stumbleupon recently announced that it signed up its 10 millionth user, and the company says it has been growing in other ways; according to a blog post, the number of advertisers has climbed by 20 percent, and the company’s headcount has grown by over 50 percent in 2010. The site recently launched iPhone (s aapl) and Android (s goog) apps as well. A report from Statcounter on social-media traffic shows Facebook is far and away the leader in referrals to sites that use its analytics service, with about 63 percent, and Stumbleupon is in second spot with 16 percent.

Related content from GigaOM Pro (sub req’d): Why Google Should Fear the Social Web

Post and thumbnail photos courtesy of Flickr user Andrew Poynton