I suggest you buy new one (get V3 if possible). Tamagotchis are small and easy to lose if neglected or out of pure carelessness (we all do), so it'll be only good if you have super memory.
Otherwise, just buy one straight from a shop (probably the same shop you bought from) and if you have spare $, better buy lanyard (a neck strap).
Yes, loosing your tama happens alot to many different people. Especially me, I was very sad when I lost my tamagotchi by being a bit careless and forgeting I put it in a different place. Just keep looking for it, and I hope that you'll find it soon.
Well, my brother lost his v3 about a month ago. I found it this morning! I was just looking for a brush...when it popped out of no where. Maybe that will happen to you. Look if you left the sound on (I don't know if you did) there is more of a possibility that you will find it. If you didn't just try to re-trace your steps. If that doesn't work...well...try to look everywhere you can. Oh! Here's a trick! where was the last place you saw it? It's a possibility that it is there.