How to resolve this issue ?
To move Apps to External Storage,
1. Goto Settings
2. Goto Applications
3. Look for the App you want to Move
4. Now you should see, Move to External Storage if the App is installed on the Internal Device (If it says Move to Phone/System Memory then the app is already installed on the microSD card) .
Note that these steps may vary depending upon the Android OS version you are using (GingerBread, HoneyComb, IceCreamSandwich, Kitkat or Lollipop)
Why Can't we move WhatsApp, Facebook to External Storage ?
You may see Apps like WhatsApp, Facebook cannot be moved, the reason is they use certain App permissions that are important for their features that does not let it install it on external storage.
If you read WhatsApp Official blog on this you would see,
Moving WhatsApp to your memory card (microSD card) is not possible at this time.
We are working on improving our application size and memory utilisation. There are technical hurdles that do not allow us to move our application to the microSD card. In the meantime, we recommend that you help make room for WhatsApp by moving as many other applications and media files as you can, to your microSD card.
Is there a way ?
The only way this can be doing is by having access to Super User and for this you need to get your Phone rooted which is not recommended.