Ah ok. I've never used Whatsapp, so didn't know they haven't updated their app to support KK. But looks like you need the actual Whatsapp+ app installed to be able to theme the stuff you are looking for. It doesn't appear to be in the Play Store, and I am not totally sure of the origins, so am hesitant to post the link here to it where I found it. If you need more info, just PM me.
Need some help, advice, something fixed? Hit me up on Hangouts @ es0tericcha0s
Now offering unlocking services - including many Sprint phone unlocks! PM for details!
HTC Droid Eris / Motorola Droid / Samsung Galaxy S Fascinate / Motorola Droid X / LG G2x / HTC Evo 3D (x2) / Samsung Epic 4G Touch (Sprint S2) / HTC Amaze / Samsung Galaxy S3 (International) / Samsung Galaxy Note 2 / Nexus 4 / HTC One / Samsung Galaxy S4 / Sony Xperia ZL / Nexus 5 / OnePlus One (64 GB)