I logged in to 'Find my phone' through my laptop, but none of the option like lock / locate / ring my phone (even if it's at silent mode) seem to work, always a message like "try again later" displayed. Though I tried ringing with other phone (and websites) it ringed but since my phone, was on silent mode, I couldn't find it. How can I make that feature (ring my phone even if it's at silent mode) work? Or is there any app which can turn my ringer on? (like there are in Android phones such as Where's my droid, Agastay etc)
There are options on the phone (in settings > find my phone) that improve the ability to find the phone before you lose it:
There are two options - one to use push notifications instead of SMS to receive alerts; This can be useful if your phone is in an area of poor mobile reception, but is on a WiFi network. The other option allows the location to periodically be saved, which you can then see when you log in with the same Microsoft account at https://account.microsoft.com/devices
With both options enabled, when logging on to the website, the phone will attempt to be connected, and GPS fix will be attempted to update the phone's location on the map.
You also have the option to get the phone to actually ring (even when on silent), Lock the phone (if you left it in a café and you think you'll get it back), or Erase the phone (if it is stolen, all your personal information can be removed)
Even if you didn't have those options available, the options should still work, but will be initiated via SMS, which will require network coverage, and text messaging rates may apply.
Of course, if your phone has no data connection, or has run itself flat, your only option is to retrace steps, and fingertip search :(