When Maniac Magee arrives in Two Mills, he doesn't have a friend in the world. Not even an imaginary one. So, is he searching for friends or a family? Can you have one without the other? The friends he makes and the friends he almost doesn't make (Mars Bar, anyone?) are important stopovers on his journey to a family. In fact, you could even say that, since none of the family that Maniac collects over the course of his journey is related to him by blood, his family ties all begin as friendships. Learning the give and take, how to trust and treat people, is what lets Maniac ultimately find his family and trust in their love—and it's what gives Maniac Magee its happy ending.
Maniac isn't always the best friend, especially to Amanda. The isolation he experienced living with his freezing cold Aunt and Uncle has left him more than a little self centered, and sometimes he has trouble recognizing what others are feeling—a pretty important part of friendship.
Without friends, Maniac wouldn't have family. His success at meeting people and getting them to like him means more than how many Facebook friends he could have: it determines whether or not he's going to get a family.