Benji, as Builder G mentioned, if you go to your 'friends' list in the game (viewed in the 'Play Friends' mode, online players will be listed first and have a green dot on their profile image. This already exists in the current build. –Lee@SMG
Builder G –As of Jan 15, we've detected a bug on the add friends mechanic that will be resolved this month. You can though still add friends. If you have any questions at all, send us a support request and I'll be happy to take you through any issues or detailed feedback.
If you have specific ideas for how to make it easier please add here or send to us directly via a support request.