The rapper 50 Cent is among the legion of stars who have recently embraced Twitter to reach fans who crave near-continuous access to their lives and thoughts. On March 1, he shared this insight with the more than 200,000 people who follow him: “My ambition leads me through a tunnel that never ends.”

Those were 50 Cent’s words, but it was not exactly him tweeting. Rather, it was Chris Romero, known as Broadway, the director of the rapper’s Web empire, who typed in those words after reading them in an interview.

“He doesn’t actually use Twitter,” Mr. Romero said of 50 Cent, whose real name is Curtis Jackson III, “but the energy of it is all him.”

In its short history, Twitter  a microblogging tool that uses 140 characters in bursts of text  has become an important marketing tool for celebrities, politicians and businesses, promising a level of intimacy never before approached online, as well as giving the public the ability to speak directly to people and institutions once comfortably on a pedestal.