Square, a start-up from a co-founder of Twitter, said Tuesday that Virgin tycoon Richard Branson has invested in the mobile payments company. Square, which allows anyone to accept credit card payments on a mobile device, did not reveal how much the British billionaire has invested in the San Francisco-based company launched last year by Twitter co-founder Jack Dorsey. In a statement, Virgin said Branson was interested in Square\'s \"rapid growth and novel technology.\" \"I\'m very passionate about helping people start and grow successful businesses, and Square is an incredible technology that inspires and empowers everyone to be an entrepreneur,\" Branson said. Square, which makes a free credit card reader for the iPhone, iPad, and Android devices, recently closed a $100 million round of financing led by venture capital firm Kleiner Perkins Caufield & Byers. Square said Tuesday that it has shipped more than 800,000 card readers to merchants and is processing over $2 billion in payments a year.