how can i find a person online for free?

im trying to find my adopted sister who i havent seen sib=nce i was 3 and im about to be 16 now she ran away when she was old enough and i am adopted as well and i want to know who i am and where i came from so if anyone at all can tell me a great way to find someone please please help or if you know her plz plz plz tell me… her name is Stephaine Jean Hall… shes 26 or 27 and lives in Baton Rouge louisiana i think plz plz plz help me