D.B.
Local mental health agency. Town department of Family & Children's Services. Private psychologist or psychiatrist - ask the family physician for a referral to someone who specializes in this and who accepts the medical insurance covering the person you are talking about. Is this an adult or a teen? Services vary based on the age of the person and who's paying for it. If it's a teen or college student, there are referrals available through the school or college psychologist.
Any addiction requires professional help. It's not something that a friend can solve, no matter how well meaning. It's not something that can be helped by going to another website. There are support groups available for families and friends though. Any of the above resources can help. NAMI (National Association for Mental Illness) can also make referrals - and don't let the term "mental illness" scare you off because it covers all kinds of disorders of varying severity, including depression and addictions, and so on. Often, an addiction has other components to it, including depression or anxiety, so getting treatment for the whole person rather than one aspect of the behavior is a good idea.