With Kleiner funding, Twitter’s valuation climbs to $3.7 billion

Folks who had a hard time believing that Twitter was worth $1 billion a year ago are going to have an even harder time swallowing the company’s new valuation.

AllThingsDigital’s Kara Swisher reports that Twitter just raised a $200 million round that valued the company at $3.7 billion.

In a company blog post, CEO Dick Costolo confirmed that the company has raised a new round from Kleiner Perkins Caufield & Byers and existing investors. (Kleiner partner John Doerr recently said that his firm was wrong to turn Twitter down in its early days). And Twitter has two new board members — Mike McCue, former CEO of Microsoft-acquired TellMe and currently CEO of Flipboard, and David Rosenblatt, former CEO of Google-acquired DoubleClick. (The post doesn’t mention funding amount or valuation.)

Earlier speculation has placed Twitter’s new valuation at $3 billion, which led VentureBeat’s executive editor Owen Thomas to ask (since it’s all speculative math), “Why not $10 billion?”

Costolo titled his post “Meaningful Growth”, and he starts off with a list of numbers showing Twitter’s growth for 2010: 25 billion tweets, 100 million new registered accounts, and growth from 130 to more than 350 employees.

What’s missing is any mention of revenue. It has only been a few months since Costolo declared that Twitter has “cracked the code” on advertising, and co-founder Ev Williams said more recently that the company is still exploring business models.

Earlier today, the company declared, “It’s Business Time” and unveiled an upgraded website at business.twitter.com, including pages highlighting its advertising products (Promoted Tweets, Promoted Trends, and Promoted Accounts). But even then, each product is described as “in beta with a small selection of advertisers.” If you want, you can fill out a form — not to place ads, but so Twitter can notify you when the company is finally ready to accept your money.