ok.. it looks like the coin really disappeared..
thanks to juhapekka, who looked for the coin, and another special thanks to Döschwo, who also traveled to the Collosseum looking for the coin.
i made a new coin, with the same tracking number.
it was made with a mill out of a block of aluminium. the finished part then was powder coated (even with location based coloring ;-)). unfortunately the color particles somehow floated around and the tux-coin has some sort of Pollock-Style on it ;-).
The coin will continue it's journey soon and you can log it again on geocaching.com.