I am assuming that all the crevices and back alley ways of the earth have been reached and that we will find no more hidden tribes. I did read an “OUTSIDE” magazine article of a lost tribe and few months ago but came to the conclusion that the indigenous people were trying to put something over on these western people for monetary gain.
Anyway, the question is, when did we find our last “lost” tribe?
We haven’t yet - otherwise it wouldn’t be lost… 
sorry, carry on…
I was going to say something similar by urging the OP to change the title from “last” to “latest” so that the question could be answered with less ambiguity.
As best I can tell, there’s no “last” anything. If I’m wrong, what is there a definitive “last” of or to.
It’s like the last word in this thread is “that” but there will probably be another one after that.
Alrighty,
What is the latest unknown tribe to be discovered?
or
What was the last “lost” tribe?
“Lost” meaning a group of people not having contact with the rest of the world.
Before anyone brings up the Tasaday, let’s remember that their standing as a “lost” tribe has been thoroughly debunked. I suspect the answer to the OP’s question will be some tribe in Brazil or Papua New Guinea.
http://www.straightdope.com/columns/040109.html
May I be the first to vote for the Mole People?
I think Pitcairn or Easter Island may have been the last absolutely isolated group. Most of the Brazilian and New Guinean tribes are known to their nearest neighbors, if not Westerners in general. But I seem to recall a new language family having been discovered in New Guinea not long ago.
There were no inhabitants on Pitcairn when Fletcher Christian and his band of merry men and women arrived. And Easter Island was discovered by Western explorers in 1722, long before the Amazon had been fully explored (if you can even say that the Amazon is fully explored today). I’ve seen film footage from the 1930s of anthropoligists making first contact with a tribe in Papua New Guinea, but I suspect there have been some tribes “discovered” since then.
My question is, how may other unknown tribes are still out there undiscovered 
Eighty-two.
I for one welcome our new Molemen overlords.
National Geographic had an article a few years back about the search for an uncontacted tribe in the Amazon. They were trailing after the tribe, trying to contacting them. They know little about these people other than a general census from the size of the campsites they leave behind. (They also found a ritual grass mask and some blow darts.)
Found it: It’s from the August 2003 issue and is unsurprisngly titled: “Hidden Tribes of the Amazon.”
Oh. My. God. I wish they had known how to write. Would love to have read their history in their own words, isolated as they were from Western and Eastern influences. Can you imagine?
Sure I can:-
“History of the Pirrinpi Tribe, Day 4,695: Ate roots and berries today. Again. Bathed in river, don’t feel much cleaner than before. Chief Jeff bitten by spider, think bite turning gangrenous. Cannot wait to make contact with West and get a decent pest-control service out here. Next week tribal elders say we’ll have a Wet Loincloth Contest to decide who gets photographed for cover of National Geographic.”