There are several ways to find and add friends.

If you know your friend’s Nanobit ID you can add them simply by entering their ID when you’re on the friends list. (Tap on the icon the lower left corner, then tap on Friends.)

When you’re at someone else’s premiere, you’ll find other guests who are friends to the organizer of the premiere. Also, you might occasionally encounter other players' characters on the street. If you want to add any of them to your friends list, simply tap on that person and after a short conversation you can send them a friend request.

You can also add new friends from the star list. Visit somebody from there, and tap on the "Add" icon at the bottom.