If a sports team tweets in the Phoenix area and no one is around to hear it, does it make a sound?

All 122 teams in North America's four major professional sports leagues have official Twitter accounts. But the number of followers for each team on the social-media site varies widely. The most-followed teams are perennial winners in big metropolitan areas. Topping the list for each sport, as of Thursday afternoon, are basketball's Los Angeles Lakers (2.98 million followers), baseball's New York Yankees (822,000), football's...