It's really a sad story when your iPhone get lost/stolen: you lost a phone that's worth hundreds of dollars, and you need to spend another hundreds of dollars buying a new one. What's worse, a thief may now has the access to all your privacy and personal data stored on your phone! In order to keep your iPhone data safe when it is lost/stolen, there are some steps you can take beforehand/afterward.
First and foremost, keep in mind that passcode is the basic security measure to protect your privacy on your iPhone. After setting the passcode, the one who want to access your phone will need to enter it. You can set a passcode to your iPhone at any time (would be best if you set it before it's stolen), and even if your phone is lost, you can still use Find My iPhone to set a passcode over the Internet.
The most effective way to ensure a thief cannot get your data is to set your iPhone automatically erase all data after 10 failed passcode attempts. However, if you're not good at remembering passcode, you should be careful in using this feature.
Find My iPhone is a free part of the iCloud, which can largely help you locate your iPhone when it is stolen/lost. Remember to enable it on your iPhone before it is lost, so that you can:
a. Locate your phone on a map via GPS
b. Display a message on the phone to show where to return it
c. Make your iPhone play a sound (useful if it's nearby)
d. Remote lock via passcode
e. Erase all data over the Internet
Apart from Find My iPhone, there're lots of other third-party apps that can help you track down your lost/stolen iPhone.Some of these apps may charge annually/monthly, while some may not. They provide you an alternative way and increase the possibility to find your phone.
Today, an iPhone can be of great use in fulfilling your digital life with different apps installed. You may have connected lots of accounts with your iPhone, including email, iTunes, credit cards, Paypal and other online banking, etc. Thus, in orther to limit the problems to your phone than let a thief steal from you even more, once your phone's been stolen, you'd better change your passwords IMMEDIATELY!