When I was a kid I heard rumors of video of an entire tribe in Papua New Guinea accepting the Gospel message all at the same time and then breaking into a massive celebration that lasted several hours. I saw a portion of the video several years later. For some reason it just occurred to me that the video would now be on YouTube and I found it tonight.
This will give you a good idea of an evangelism technique used by New Tribes Missions. They exclusively seek out tribes which have never heard the message of the Bible.