SAN FRANCISCO — Twitter Inc.'s founders now have a billion-dollar baby, and they seem determined to raise it without a corporate parent.

That was the message underlying yesterday's news that Twitter has lined up $100 million to finance its operations while founders Evan Williams and Biz Stone plot ways to make money off one of the Internet's most popular communications tools.

The investment values the 3-year-old company at $1 billion, even though it has yet to generate any meaningful revenue, let alone profits.

Twitter itself didn't provide specifics about the size of the investment, saying only it involved a significant sum. A person with knowledge of the negotiations confirmed the amounts to The Associated Press on condition of anonymity because the parties had agreed not to announce the specifics.

Williams and Stone declined an interview request.

The latest stakes were sold to three of Twitter's existing investors — Benchmark Capital, Institutional Venture Partners and Spark Capital — and two new shareholders, Insight Venture Partners and T. Rowe Price.

San Francisco-based Twitter had previously raised $55 million, with the latest infusion of $35 million coming just seven months ago.

With so much money in the bank, Twitter now has the means to buy more computers and keep improving the reliability of its outage-prone service. It can expand its work force of 60 employees without feeling the pressure to sell to a larger company.

"This is a smart move by Twitter because it buys them more time to capitalize on their momentum and come up with a business plan," said Ken Marlin, a technology investment banker in New York with Marlin & Associates.

Twitter turned down a $500 million buyout offer from Facebook Inc. last year and both Google Inc. and Microsoft Corp. were rumored to be inquiring about a possible acquisition earlier this year.

Williams didn't refer directly to any suitors in yesterday's blog posting, but he indicated Twitter wants to see how far it can go on its own.

"It was important to us that we find investment partners who share our vision for building a company of enduring value," Williams wrote. "Twitter's journey has just begun and we are committed to building the best product, technology and company possible."

For now, Williams and Stone have been focusing on building Twitter's audience.

Twitter has more than 54 million worldwide users who share their thoughts, activities, Web links and other information in messages no longer than 140 characters. Just a year ago, only 4 million people were tweeting. By 2013, Twitter hopes to have 1 billion users, making its service "the pulse of the planet," according to internal company documents leaked on the Internet this summer.

If Twitter is unable to make enough money to pay its bills, Marlin thinks the company would still fetch a substantial price, although probably not $1 billion.