The National Human Trafficking Resource Center, through its Polaris Project, is an excellent organization with a multitude of local, State, and National resources. They are also an excellent resource for international resources.
Organization Name: Polaris Project
If you are aware of a child known to be missing, please contact the National Center for Missing & Exploited Children (NCMEC). Since 1984, NCMEC has been a national leader in providing resources relating to missing and exploited children.