This is a very important request as drugs can destroy a peron's life.
First, I would say that most important resource or support to help a young person to stop taking drugs is to talk about it openly. Moreover, there should not be a threatening or judgmental stance. Trust is central as a first step.
Second, there are programs in school, if a person is a student. High schools and universities have programs and people in place to help in this area.
Third, there are organizations that specialize in this area. For example, The Alcohol & Drug Recovery Center specializes in helping people. Their website is: www.TheRecoveryPlace.net/Recovery.
Finally, many churches or bodies of worship has staff that help with drug addiction. For this reason, you might want to call the local community of faith. And as a general rule of thumb, the larger the organization, the more resources they will have.