What? You placed your android phone some where and forgot again? And its in silent mode?
No problem you can find it easily by following the steps below.
On your computer open Google Play https://play.google.com in browser.
Press the Settings icon at far right of the page.
Click on Android Device Manager.
Next screen should list all your phones registered with Google Store. Choose the one you want to find. Click on Ring button and the phone will ring with full volume even if it was in silent mode.