StumbleUpon announced that it has raised a new $17 million series B round of funding, which the company will use to invest in the company’s discovery technology, expand to new platforms, and grow its employee base.

The new funding comes from Accel Partners, August Capital, DAG Ventures, First Round Capital and Sherpalo Ventures. The last round  was led by Accel Partners, August Capital and Sherpalo Ventures.

“We are excited to have DAG Ventures join our existing investors in this new round of financing,” said Garrett Camp, StumbleUpon CEO and co-founder. “With this new investment, we will make it even easier for people to find interesting and relevant content on the Web, whether they are on their desktop, mobile device or even TV.”

“StumbleUpon continues to grow quickly and deliver on its ambitious goal of powering personalized content discovery across all media and platforms,” said Sameer Gandhi, Partner, Accel Partners. “Content discovery is a significant opportunity, and we are excited to continue to support the leading company in the space.”

StumbleUpon finally came to iPhone and Android last year, breathing a bit of new life into the service for a lot of users. The company also recently made efforts to improve its video discovery service.

One of the most interesting things about StumbleUpon is that while it doesn’t get nearly the attention of other social platforms like Twitter and Facebook, it is cited time and time again as the biggest provider of social media traffic to websites.

Most recently, a report in January from StatCounter found that StumbleUpon was the top social media traffic source in the U.S.

It will be interesting to see where StumbleUpon expands next. With the emerging tablet market, my guess is that we’ll see some cool new stuff designed for these platforms.