Tomodachi Life: How does it work with the travelers?

I've heard that you can pick up travelers from other islands or send them away. How exactly does it work? Via street pass? Or do you have to be friends with others? I do not currently have any friends who play Tomodachi Life or have a Nintendo 3DS. Maybe I can exchange my friend code with one of you. If that brings anything.

This works via streetpass. All you have to do is close your Nintedo and walk around the city, go to a friend and you'll be greeted by a variety of Miis.