They are not. It is only ten of the original twelve Tribes that went lost, not all twelve. Jews are descended from the ones that didn't go lost. The reason that the Ten Lost Tribes are called that, is because they were carried off into exile by the Assyrians some 2600 years ago and did not return. Their whereabouts is unknown.
The great majority of Jews today, some 80% or so, are descended from the tribe of Judah (plus converts and descendants of converts). The remaining 20% include Levites (from the tribe of Levi), Cohanim (also a part of the Levites), the entire Tribe of Benjamin, and a small percentage from every one of the remaining tribes. (When the Ten Tribes were carried off into Assyria and didn't return, a few of them had already mixed into the tribe of Judah before that, through marriage. Also, the Talmud relates [Megillah 14b] that, one century after the Ten Tribes were exiled [and their location was still known], Jeremiah journeyed to where they were and brought some of them back to Judea. Thus, today's Jewry includes a small percentage of every one of the Lost Tribes. (See for example the Talmud, Pesachim 4a.)
As to the location of the bulk of the lost Ten Tribes, because of the lack of a continuous tradition in this particular matter, we can only speculate. Some well-known claims, such as the suggestion that the Native Americans or African Americans are the Lost Israelite Tribes, we can confidently dismiss offhand; and DNA analyses have also debunked such ideas. Other claims, such as that which has been suggested concerning the Pathani (Pashtun), are less far-fetched but must for the time being remain nothing more than a guess.
See also:
JUDAH and BENJAMIN.
hey
There were 10 tribes, but they weren't lost. What happened was, during the Babylonian captivity of 586 BCE, the 12 tribes of Israel were expelled from the land and sent to Assyria. After 70 years, 9½ of those 12 Tribes had just assimiliated into Babylonian society, leaving only 2½ tribes returning to Israel.
Nova - 1974 Lost Tribes of Israel 27-17 was released on: USA: 22 February 2000
Edward Hine has written: 'Forty-seven identifications of the British nation with the lost Ten Tribes of Israel' -- subject(s): Lost tribes of Israel
The Ten Lost Tribes of Israel were ten of the twelve tribes of the Ancient Israelites who were defeated by the Assyrians and forcibly deported (as was common Assyrian custom). They lost their distinctive Israelite heritage. There is some speculation as to whether some of the lost tribes of Israel were African, but most people believe that the Lost Tribes of Israel merely lost their distinctive heritage and became part and parcel of other ethnic and religious groups in the Middle East.
No. All twelve tribes are from Israel. They are known as the twelve tribes of Israel, they all descend from Abraham's grandson who was named Israel. There are some offshoot religions that claim to be one of the tribes, or a "lost tribe" of Israel, but blood tests have proven they do not descend from Israel.
The Ten Lost Tribes of the Israelites.
The scattering of the ten tribes of Israel, often referred to as the Assyrian Exile, occurred around 722 BCE. This event took place when the Assyrian Empire conquered the northern kingdom of Israel and deported many of its inhabitants. As a result, the ten tribes—often called the "Lost Tribes of Israel"—were dispersed and largely assimilated into surrounding cultures.
The Ten Lost Tribes of the Israelites.
The Ten Lost Tribes. http://judaism.answers.com/jewish-history/where-are-the-ten-tribes-where-is-the-ark-of-the-covenant
Israel Worsley has written: 'A view of the American Indians' -- subject(s): Origin, Indians, Lost tribes of Israel