Re: the missile . . .
Missiles fired from the Buk system travel at approximately 3200km/h - or around 3000 fps.
The missile doesn't impact the target - but detonates in close proximity.
When it does detonate - it doesn't "stop" in the air - instead its momentum continues to carry it along its trajectory.
While some parts of the missile may impact the target and fall with it - many pieces of the missile will continue to fly past the target.
So - I highly doubt that you will find many "pieces" of the missile scattered about the debris. The plane came apart in a relatively wide area - and I suspect most of the parts of the missile (if it was a missile) came down some distance away from the aircraft. Best chance to find pieces would likely be if any are imbedded in the aircraft.
These objects all fell from high altitude and momentum carried them downrange of the point of impact (even if only slightly). The simple fact that the two were traveling at different speeds will create some distance between the debris field of the aircraft and missile.