There's two uniquue things that most cell phones have.
1 - Even though it's on silent, the phone will still vibrate. The house have to be very quiet. You call your cell phone and start looking for it. You should hearing it buzzing from the vibration.
2 - Wait till the battery goes dead. It will start to make a noise. The noise varies depending which phone you have. Usually the noise is couple of beeps every so often.
So that's how you find your phone. Like the other posters said, if you lost it for few weeks, it's already too late. The battery is now dead.
Did you hear any strange noise from your house or your friend's house? If not, maybe you didn't loose it there. You probably lost it someplace else and now someone else have it now.