Looking for birth relatives

I was born on July 22,1966 Detriot, Michigan. My mother was at the Chritedon Materinity home until my birth. I do have some information on my mother but have been unsuccessful in locating her thus far. My mothers mother and 2 siblings were killed in a car wreck ? years before my birth. My mother was injured and one sister lived after the wreck. My mothers pregnancy was hid from most everyone but her sister did visit her at the maternity home. My Grandfather raised Palimino horses, was a tree surgeon and a township superviser. My father left my mother before my birth and married another woman. Any information would be appreciated. My adoption records are in Macomb county, should I hire a intermediary?