Hi is wondering how you would find some one if you think they were ever in drug treatment or to find some one?

Hi i was wondering how you find some one if ever they were in drug treatment or just to do research on finding some one you have not seen in 20 years or so.
They were homeless or lived only three place maybe at maxs it's a family member who think is still in the same town i am from but has not phone number or address or anything as for as a life goes so now where do i go from there ?

: http://alcoholdrugstreatment.info/hi-is-wondering-how-you-would-find-some-one-if-you-think-they-were-ever-in-drug-treatment-or-to-find-some-one