What are some ways to overcome social anxiety/social avoidance disorder?

My cousin seldom if ever goes out- he works, then goes home and stays in. he's only 27, and a great guy- fit, good looking, but utterly lacking in self confidence when it comes to meeting people. i really want to help him- what are some ways he can break out of his rut? is social anxiety and social avoidance conditions that need to me treated with medication, or can they be overcome by changing behavior?