How to create ASP.net identity tables in an already created database using code first?

My application has been in development for about a month. I now decided to use ASP.NET Identity. I already have the view models for identity but need to create the tables. I was thinking and I am not exactly sure why I do not have the tables already if I have the view models?? I have drop create on in the initializer with my own custom context, I just need to know how to get EF to build the included Identity tables for users and roles? I looked around and none of the posted answers seem to be what I need?