Sept. 26 (Bloomberg) — Twitter Inc., the social-networking site used by everyone from Oprah Winfrey to British royalty, received venture financing that values the company at about $1 billion, according to a person familiar with the matter.

Twitter received $100 million in the deal, according to two people who wanted to remain anonymous because terms of the agreement are private. Twitter announced the investment on its blog, without citing an amount. The investors included T. Rowe Price Group Inc., Insight Venture Partners, Spark Capital, Institutional Venture Partners and Benchmark Capital.

Given a $100 million equity investment, a $1 billion valuation would mean that investors acquired a 10 percent stake, said John Taylor, vice president of research at the Arlington, Virginia-based National Venture Capital Association. Twitter and the people familiar with the deal didn???t say how investors arrived at the $1 billion. Setting the value of a company involves assumptions about how investors will earn a return, possibly through an initial public offering or acquisition.