Returning a record with a string in ember

I am trying to implement a search function where a user can return other users by passing a username through a component. I followed the ember guides and have the following code to do so in my routes file:

this.store.find('account', { user_name: params.userName })

This code, however, throws me the following error:

"You cannot pass '[object Object]' as id to the store's find method"

I think that this implementation of the .find method is no longer valid, and I need to go about returning the object in a different manner. How would I go about doing this?