Answer:
If it was inside a house:
Have you checked the last places you remember having it? If not, maybe recall if some friends came over and maybe took it by accident? If you have a pet, maybe it has something to do with it.
If it was outside a house:
Where do you remember going when you lost it? Maybe check the lost and found in your community (most likely at a police station or a school) If it was lost in a school, ask a teacher or a principal to help look for it. Maybe a person who was cleaning found it and placed it somewhere.
Good luck, hope you find it!