Facebook has opened its first sales office in Africa, the company said on Monday.In a statement, Facebook said the sales team in Johannesburg will initially focus on sub-Saharan Africa to capitalize on Africa's 200 million internet users - 120 million of whom are already Facebook users, with 80 percent connecting via mobile devices."Mobile is not a trend, it's the fastest development in communications we've ever seen," Vice President Nicola Mendelsohn said. "This couldn't be more true in Africa, where so many people are mobile-only."She added: "Facebook is already a central part of people's lives in Africa and with more than 1 billion people in Africa, we want to do more to help people and businesses connect."