Are there any online Warrior cats MMOs?

Yes, you can. There are several roleplay sites based on Warriors, including one by Erin Hunter. There is also an official site by Erin Hunter with two different quests and quizzes. Also, you can play quizzes to find out what your warrior name is or your clan and things like that.

You can also go on sites and roleplay Warriors. There are various different ways they are set up. i will list a few here:

Warriors: New Power

Warrior Cats RPG

Clans of Twilight: Dog vs Cat RPG

Links are below. I own one but the other two sites are also great and I recommend them.