Of course the Americans believe in them, just look at how many Americans actually believe that one day Jesus will walk down their streets!
Bigfoot is just another silly story, I'm sure if they existed some gun happy American would have found one and shot one by now.
When someone can show me a skeleton of one, (there must be thousands of them lying around in the American wilderness) then I will believe, until then it will be like the bible, just nonsense!