• by Mark Walsh  @markfwal, February 13, 2009

Twitter may not have a business model yet, but that hasn't stopped the hot social media company from raising additional capital. The micro-blogging service on Friday announced new funding from Benchmark Capital and Institutional Venture Partners.

While Twitter did not disclose the amount, TechCrunch is reporting the startup raised $35 million in the third-round financing that also included existing investors Union Square Ventures and Spark Capital.

Twitter co-founder Biz Stone indicated in a Friday blog post that the financing would help speed the company's efforts to start making money from its wildly popular service.

"We are now positioned extremely well to support the accelerating growth of our service, further enable the robust ecosystem sprouting up around Twitter, and yes, to begin building revenue-generating products," wrote Stone. "Throughout this year and beyond, our small team will grow much bigger to meet the challenges and opportunities ahead."

In an interview with U.K.-based Marketing magazine this week, Stone suggested that the company is exploring charging for commercial Twitter accounts and creating revenue-generating features that capitalize on how brands use the service as both a marketing and customer-service tool.

To date, Twitter has raised a little over $20 million in venture funding. Rumors circulated at the time of Facebook's failed acquisition of Twitter last fall that put its valuation at $250 million. According to Stone, active Twitter users have increased 900% in the last year. A report by the Pew Internet & American Life Project released Thursday estimated that 11% of U.S. Web users are actively Twittering.

The company's newfound status as a cultural phenomenon was confirmed this week by the "Shorty Awards," an awards ceremony held in New York on Wednesday night recognizing the best "tweets," the 140-character messages sent via Twitter.