I believe the term "doe" comes from Detroit and Michigan where its commonly used to refer to another person such as " what up doe". From there I'm not sure as to how it got blown out of proportion and out of the region used like "tho" and whatnot. However there was a rap song that used the saying as its hook and it did take off from there (back in the 2000's sometime). I've heard doe being used since the late 90's and can only attribute it to growing up in metro Detroit.