Can the police do anything? If not, what can I do?

Yesterday night, some guy approached me to hit on me while I was on my way to the meeting place (In front of a school) for Drivers Ed. I told him I'd like to be friends, and went on my way. While waiting at the stop, my drivers ed partner arrived. The boy who previously tried to hit on me, saw my friend and punched him from behind after asking for the time. He, along with his 3 other friends began to beat my friend up while one of the guys stole my iPhone 5 and ran off. We called the police and reported everything.

I have a GPS tracking app on my iPhone. I know where it is, in what house, and called the cops. My mother and I met with the police at the located house. And the police knocked at their door. The thief of course did not answer the door, and the police said they can do nothing more. Are you serious? That's it? Can the police really not do anything else to help me? These kids beat up my friend, and stole from me. Is there anything I can do?

Added (1). My friend is going to see the doctor today, and his family is going to press charges. So I just need to know what I can personally do.

That's life.

The police officer was lying. If the tracking app shows that the iPhone is in that house, he can ask a judge to give him a search warrant to recover the phone.

Complain to the police. Ask to speak to a supervisor (someone who is at least a sergeant). If that doesn't work, contact the prosecutor's office. They usually have a victim's services department where you can talk to someone.