SAN FRANCISCO – Popular micro-blogging site Twitter has raised at least $50 million on a valuation of $1 billion, according to TechCrunch.

TechCrunch reports that sources say a primary investor may be New York-based Insight Venture Partners.

It certainly has the muscle. It raised more than $3 billion since 1995.

TechCrunch says its not clear if Twitter is capping the round at $50 million.

The buzz on the deal heated up as Tweets spread the news Thursday morning.

Most stories noted that the news comes on the heals of Facebook’s announcement that it had surpassed 300 million users and was cash flow positive ahead of schedule.

Speculation abounds as to whether the two social networking sites, which have rocketed to incredible popularity in recent months, can maintain their momentum.

TechCrunch: http://bit.ly/w9nhF

ReadWriteWeb’s take: http://bit.ly/14htgE

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