I use a "Models" folder alongside Controllers and Views. The same one which is empty in your project (I don't use Areas).
The "M" in "MVC" model goes in a separate assembly. The only models in the web assembly are presentation/edit models.
Inside the Models folder, there are subfolders by namespace as usual. So I have:
Vertex.Data (Assembly with repositories, etc.)
Vertex.Web
Controllers BarController FooController Models Bar BarListItem Foo FooDetail FooListItem Views Bar Foo Shared
...etc.