StockTwits, a real-time community-powered site for investment information, secured a $4 million venture round from existing investors the Foundry Group (which recently closed a $225 million fund) and True Ventures, we’ve learned from co-founder and CEO Howard Lindzon. The site has raised $8.6 million to date.

The new funds will be used to expand the engineering team and further develop the site, said Lindzon.

While he would not comment on the site’s current valuation, the site has tapped into multiple revenue streams--mostly ad-based--since day one.

As the name suggests, StockTwits was born as the perfect marriage of Twitter and the stock market. Searching the site for a ticker symbol (like GOOG), for example, summons a real-time stream mostly composed of posts from Twitter and StockTwits itself. To the right of the stream appears a chart displaying Google’s stock performance over the day, week, or month.

StockTwits has been looking well beyond these two most basic functions in the past year. In January, the site acquired financial news site Abnormal Returns to incorporate the site’s news into the stream. StockTwits then partnered with SecondMarket in August to let users post about private stock in addition to public stock.

Just a week ago, StockTwits launched an iPhone app that brings in the main site functionality, charts from Chart.ly, and news from Abnormal Returns.

While it seems like most reputable financial web services offer real-time stock data, it’s refreshing to see at least one company incorporate that data with the most obvious related network: real-time communication.