Can Twitter make this announcement under its 140-character limit? After $100 million in venture-capital funding was provided by investors to social-networking site Twitter, the company’s value may have reached an astounding $1 billion, according to a source familiar with the deal. In addition to giving investors a 10 percent stake in the company, the infusion means that people around the world will continue to have the opportunity to announce each time their dog does something cute. How Twitter, which has been rapidly growing since it began in 2006, will use the new capital to generate revenue has not been announced, but this month, co-founder Biz Stone announced plans to add business services such as an “analytics dashboard” and possibly advertising to the site. Included among Twitter’s 25 million users are celebrities like Britney Spears, Ashton Kutcher, and Oprah Winfrey.