Once upon a time I had Toa Metru Matau. One day, when I was about eight, half of the pieces spontaneously went missing. I got a new Matau off ebay luckily.
As for those missing pieces, I have no idea where they are but my most plausible theory is that my friend may have stolen them. He used to say that Matau was his favourite Toa and that a few of his parts were gone.