Your favorite stations are located under RADIO -> YOUR STATIONS -> Your favorites.
This view shows a summary of your RADIO activity: it shows your favorite stations and the stations you have recently listened to.
Your favorites were automatically taken over when the app was updated from version 4 to 5. Login with a user account is no longer possible from version 5. If your favorites are not displayed after the update, you could try restarting the app. Otherwise you would have to search and mark them again.
Furthermore, the song marker function has been removed from the app, as it was unfortunately not used enough. On the radio.net website, the song marker function is still available. There you can mark songs as favorites and open them in iTunes or on Amazon.