Reuters reports that Twitter is closing a round of funding that puts a value on the company of a whopping $1 billion. The last round of funding that Twitter secured was in February and valued the company at $250 million.

Sources from TechCrunch claim Twitter CEO Evan Williams told Twitter employees about the new round of funding. Social networking sites like Twitter, Facebook, and MySpace are still working hard to prove that they can make money and prove viable in the long run.

Twitter currently runs no ads on its service, but recently changed its terms of service to allow for the possibility of serving ads. Speculation is that Twitter may begin running ads similar to those that Google uses alongside it search results.

Twitter users are able to run searches from the Twitter site to look for information about specific topic being posted in Tweets across the network. Twitter's popularity is booming and this may be the right time for the company to start selling ads.

Twitter grew to 44.5 million users in June, an increase of 15 times compared to the previous year. Analyst Salil Deshpande from Bay Partners said, "When something like Twitter or Facebook becomes a cultural phenomena, it's much more than the sum of the parts. It's really tapping into a cultural shift. As the network effect increases, the value increases."

Twitter is used by a massive and varying population. President Obama used Twitter during his campaign and the service is used by celebrities, news producers, and average citizens.