Don't expect Twitter to be tweeting about an initial public offering any time soon.
The popular online communications service has raised another US$200 million ($270 million) so it can keep growing without Wall Street's help.
Kleiner Perkins Caufield & Byers, one of Silicon Valley's best-known venture capital firms, is leading the investment.
Twitter's
association with Kleiner Perkins is likely to add to the intrigue about the money-making potential of a service that each day blasts out more than 65 million short messages, or "tweets", limited to 140 characters.
Kleiner Perkins' past internet bets include investments in online search leader Google, now worth about US$190 billion, and leading web merchant Amazon.com, now worth about US$80 billion.
The venture capital firm obviously thinks highly of Twitter, which started in 2007 and has raised a total of US$360 million. The latest US$200 million investment values Twitter at US$3.7 billion, up from US$1 billion 15 months ago when the company last raised money from venture capitalists.
With so much cash being supplied by investors, Twitter's management has been able to focus on hiring more workers and adding more features instead of worrying about making money.
The San Francisco company now employs about 350 people, more than tripling its payroll since the beginning of the year.
Most of Twitter's revenue so far has flowed from deals that have given Google, Microsoft's Bing and other internet services better access to its messaging stream.
