There are plenty of 9Gag apps on the windows phone marketplace, but not the official one. But, now the Ray from 9Gag has himself confirmed that an official 9Gag app is in the making and it will be released soon.
I personally use this 9Gag app from Rudy on my Nokia Lumia 920 for the time being and it works pretty well. It has gif and video support too.
But yes, an official app would lure users from other platforms from sure.