How to get my iPhone do vibrate when locked?

I wan't my iPhone 4s to vibrate when locked when I get a facebook message. I already have checked "show in lock" or something like that under settings>notifications>facebook.
My phone is on silent and it is set to vibrate when silent and when on ring.
Can I get it to vibrate on ring and silent?

Added (1). I had it set to only vibrate on silent a couple days ago and i had my phone on silent but whenever i got a whatsapp message it worked.

Try turning vibration mode off wait a minute of two the turn it all

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