No offense, but it looks like you were neglecting the thing and it ran off. Those batteries aren't going to replace themselves and I'm sure that nobody needs to remind you that the batteries in the newer RioCar remotes aren't known for their longevity out of the box. That said, these things can get quite jealous, so if you do buy a new one as Peter suggested, it is likely to show up again. If that doesn't work, you may have to win its trust back. The hiding spots Laura suggested may turn up some clues.

Lets hope that it didn't run off with one of the Kenwood remotes...