Looking For My Adopted Brother

I am looking for my brother who was put up for adoption right after birth. My father is Carl Frederick Gerhardt and my mother is Ida Mae (Gerhardt) maiden name Rensinghoff now Ida Sroka. I was born on 12/25/60 and my parents divorced in January, 1961. I have another sister who was born on 8/27/63. I know that my brother was born sometime in between us. We are of German descent. My father lives in Kentucky and my mother lives in Illinois. We have a large family since my mom and dad both re-married. From oldest to youngest they are Cynthia (Cindy), Cathleen (Cathy), Carl, me Christine (Chris or Duff), my adopted brother (missing), Susan (Sue), Cheryl, Frank, Constance (Connie) and Craig. I did not even know that my parents gave my brother up for adoption until I was in my late twenties. We lived on Paulina St. in Chicago. My father's parents owned a bar on the first floor of an apartment building. This is no longer there. My grandparents are all deceased. I was told that the doctor and the lawyer involved in the adoption process are also deceased. I believe that my brother was given up for adoption in Chicago, IL and it was possible one that was not considered a legal adoption. I believe that he was adopted by friends of either my mother or my father of a friend of the family. My father has brown eyes and my mother has blue eyes, so my adopted brother could have either. We are mainly brown to blonde hair and have blue, brown and green eyese. I know it's not much to go on but I would like to find my brother. If any of you out there know anything that sounds like you might know something you can e-mail me. Thanks for listening, Christine F. Duffy (Gerhardt)