The area is very hard to access, but the first expedition got there by 1927 (the link about how they got there is quite interesting.) They found *nothing* except traces of an airburst. Since then many expeditions from all over the world traveled there, now expecting to find microscopic particles of the impactor, and not a solid meteorite as the earlier scientists believed. Besides, after 1945 people learned what a multi-kiloton explosion can do, and how it looks like on the ground. (Tunguska event is estimated at 10 to 15 megaton.)
For more, Wikipedia seems to have plenty of material.