Usually if you lose your cell phone, you can call it and try to locate the sound. Silent mode disables all sound and vibration notifications when you call or text the phone, making listening out for your phone impossible. Depending on the situation where you have lost your cell phone, there are numerous ways to attempt to locate your lost phone.
Determine where you last remember seeing the phone. Go to this place and look from this point to where you are now, retracing your footsteps and checking the floor thoroughly. Look in all the pockets of any items of clothing you were wearing at the time as well as any cars you travelled in; make a list of any events where you would be likely to have dropped it -- for example, tripping or falling over.
Turn off all the lights if you think you may have lost it inside. Call your phone number; your phone's screen should light up during the call and you may be able to see the glowing screen in the dark.
Scan the area where you think you may have lost it with a metal detector.
Call your phone company. Many modern phones can be located using GPS. Ask the phone company to track your phone's location for you.