Twitter has raised $200m in a funding round that valued the micro-blogging site at $3.7bn, up sharply from the estimated $1bn last year.
New backers include Kleiner Perkins partner John Doerr, who was an early investor in internet groups including Google and Amazon.
The new funding round comes less than a year after Twitter began its first serious efforts to make money.
The funding, from Silicon Valley venture capital firm Kleiner Perkins Caufield & Byers and existing Twitter investors, underscores the high hopes that investors have for Internet social networking companies.
The money will help Twitter expand the company, Twitter said in a post on its corporate blog on Wednesday.
Twitter, which had 175 million users as of September, is among the new crop of quickly growing Internet social networking services. Others include Facebook and Zynga.
Facebook, the world’s No. 1 Internet social networking company, is valued at more than $45 billion in recent stock purchase transactions on the secondary market, according to Sharespost, an online exchange for trading shares in private companies.
Investors are watching services like Facebook and Twitter closely, hoping one day to buy public shares of the company.
Twitter also announced on Wednesday that it had added two new board members: FlipBoard Chief Executive Mike McCue and DoubleClick CEO David Rosenblatt.
The moves come two months after the four-year-old company handed the job of chief executive to Dick Costolo, the architect of its new advertising efforts, a sign that making money is a priority for the service.
Twitter had raised $160 million in four earlier funding rounds, from investors that included Spark Capital, Institutional Venture Partners and mutual fund company T. Rowe Price.
