Don't risk your safety, leave finding stolen iPhones and iPads to the police
Find my iPhone, a technology that allows you to track down your iPhone, iPod touch, iPad, or Mac to the last place it was connected to a cellular or Wi-Fi network, has unsurprisingly lead to incidents of "hero complex" over the years. That's when an every day person, not affiliated with law-enforcement, decides to take crime intervention into their own hands, track down the perpetrator, and make them pay. And, tragically, sometimes that's the last thing they ever get to do. Numerous recent incidents have been collected by the New York Times, which also offers this quote from San Francisco DA George Gascón:
Some have been successful. Others have gotten hurt.
That's the most important part of the entire article. A phone is just a phone. If yours is ever stolen you might be out some money, maybe some pictures — remember to back up! — but if you chase after a criminal and create a secondary crime scene you could lose a lot more, including your life.
Phones can be replaced. People can't.
Chasing after an iPhone thief is no different than chasing after a mugger. You just don't know what kind of a situation you'll end up in. We, none of us, are the Batman. We won't always win. Justice and karma won't always come out in our favor. And even if we do, we could go to jail for our own actions.
Use Find my iPhone to track down your device if you lost it in your house or left it at a restaurant or anything else dumb like that. Leave law enforcement to the people who are trained, equipped, and backed up enough to do it properly.