My WhatsApp icon has recently disappeared from my phone completely. It's neither on the home screen, nor the main menu. When I go to the Google Play store, it shows that it's part of my installed applications. I uninstalled and re-installed the app, but it still doesn't show the main icon, so I'm unable to even open it... Even though it says it's installed on my Samsung Galaxy S2.
Things I would try:
a) Just reset the phone if you haven't done already(turn it off and on
b) Uninstall the app, remove the sd, and install it again. There might be a problem with your SD card, and if the app is automatically installed there, maybe that's the reason you can't see it
Which launcher are you using? I believe you can see the app in the settings -> applications list?