The latest cash infusion would nearly triple the total venture capital poured into the 3-year-old Internet messaging start-up, from $55 million to $155 million.
In a blog post, Twitter co-founder Biz Stone thanked the San Francisco company's new financial backers, including investment firm T. Rowe Price and Insight Venture Partners.
"It was important to us that we find investment partners who share our vision for building a company of enduring value," Stone wrote.
"Twitter's journey has just begun."
Stone did not disclose the amount of money Twitter raised, but news reports cited $100 million and noted that investors were valuing the company at $1 billion.
Twitter did not respond to requests for comment.
With celebrities, politicians and media figures using the service, Twitter has enjoyed uncanny growth over the past year, going from a little over
1 million U.S. visitors in August of last year to nearly 20 million last month.
Questions about whether the company could sustain that growth rate were partially answered this month, as data from marketing research company comScore and other Web ratings firms showed the first decrease in the size of Twitter's user base since the company gained mainstream attention last year.
Meanwhile, the company's plan for converting its massive audience into dollars still is not clear. The company continues to cling to one of Silicon Valley's oft-repeated mantras: Audience first, business model second.
Stone emphasized the company's patient approach this week when he was asked about when Twitter might start allowing advertisements — generally considered to be the company's best bet for profits.
"It'll be awhile," he said, and users shouldn't expect to see it before 2010.
Twitter has also said that it would support for-pay commercial accounts for businesses, which likely would offer customers more tools for analyzing what Twitter users were saying about their products. That feature may arrive later this year.
Twitter's last round of funding came in mid-February, when it collected
$35 million from Institutional Venture Partners and Benchmark Capital. Spark Capital and Bezos Expeditions also have invested in Twitter.
In recent days, Twitter has been adding to the slate of sites and services that are allowing users to tweet, including MySpace and AOL's Lifestream platform.
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