Twitter is planning to raise $100 million in its second round of funding this year, which would put the company's valuation at $1 billion, according to media reports citing sources familiar with the deal.
The reports say that the investors include T. Rowe Price and Insight Venture Partners, who are new investors in Twitter, as well as venture-capital firms Spark Capital and Institutional Venture Partners, who had previously invested in the microblogging Web site.
Requests for comment from Twitter were not returned.
Twitter is not publicly traded, making it difficult to put a price tag on the social networking firm. The site, which allows users to post 140-character entries called "tweets," has yet to announce a business model or revenue strategy.
That hasn't stopped Twitter from actively raising capital. In February, co-founder Biz Stone posted on Twitter's official blog about "an offer we couldn't refuse" from Benchmark Capital and Institutional Venture Partners. While the post did not disclose financial details of the "very attractive offer," it was widely reported that the firms gave approximately $35 million combined.
In July, Stone told Fortune that the company would reveal its money-making plans sometime this year. He has previously said publicly that Twitter does not need to generate revenue any time soon, since it has not yet exhausted the more than $50 million it has raised from venture capitalists.
Though Twitter has not revealed its business model, co-founder Stone announced earlier this week that the company would not raise money through advertising in 2009 as some experts had anticipated. At the 140: Twitter Conference in Los Angeles on Tuesday, Stone said it would be "awhile" before Twitter displays ads on its Web site.