I would like to put forth my experience. We forgot to take our camera when alighting at Florence; the train was bound to Naples. We had very little time left before boarding the next train to Pisa and from Pisa, the flight back to London.
We ran to the Trenitalia counter at Florence, and clearly told them the details of the location and attributes of the camera bag. The in-charge registered the complaint, and made a note of our address. Initially he was a bit hesitant to send the camera all the way to London, but somewhat agreed once we promised to pay the mail charges. He did not give us any phone number or email, but promised to contact us through email if the camera was available.
That said and done, we were not quite hopeful (especially after seeing Mattia's comment, and the numerous negative stories on the Internet on lost items in Italy). However to our pleasant surprise, the in-charge officer mailed us four days later acknowledging the presence of the camera in his office. He had somehow managed to retrieve it from the train and got it transferred back to Florence. In a few days, he mailed us our camera back after getting our credit card details in order to cover up for the postage.
I guess three things helped: one, we were travelling during the off-season, two, we knew precisely where our camera bag lay, and three, the officer-in-charge was helpful, diligent and sincere. There was literally nothing binding on him to go through all this trouble.
TL,DR: Do not lose all hope. Do not forget to register the complaint in person at the station (complaints via phone do not get registered).