Sorry, but Apple cannot help you with this one. All of us here are only end users like yourself anyways. You'll have to look for it like any other lost device. You could/should report the indicent to the police and/or talk to parents about the situation.
Who is this "you" that you're asking to give you an IP address? There's no Apple here; it's just other users in this forum, like you.
Regardless of whether the likely culprit is your brother or someone else, file a theft report with the police. Apple can't do anything for you if Find My iPhone is not active for that device.