Research on addicts shows that 90% of addicts, when approached through intervention, will accept the help being offered if they intervention is done in the right spirit. You need to make sure that everyone involved has the same goals and wants what is ultimately best for the addict, even if that means that it will be hard on the individuals surrounding that person.
There are several methods surrounding interventions. You may want to talk to a trained addiction specialist who has handled many intervention cases about which method may be right for the addict and the support group surrounding the addict. It is important to note that interventions can be held for individuals with ANY addiction. This includes alcohol, substance abuse, gambling, and more.
It is important to only have those closest to the addict involved in the intervention. This should be a safe place for the individual. They should be surrounded with people they trust and know love them. It is important that they realize that everyone comes in a spirit of love and understanding with the intention to help, not judge.
When the addict does decide that they want help it is best to get them to a residential treatment program and seek professional help.