If you have used Find My iPhone Activation Lock in iOS 7, you might marvel at its great feature. Upon the foundation, the anti-theft feature in iOS 8 is proven to reach higher level of performance. Here, I will show you the technique of Find My iPhone in iOS 8.
Before you can locate your devices, you need to set up iCloud and turn on Find My iPhone on your device. Find My iPhone requires iOS 5 or later, or OS X v10.7.5 or later.
2. Enter your Apple ID and password to log in your Apple ID. Then await validation.
3. If you log in your Apple ID at the first time, a window will pop up asking you whether to merge data on your iPhone with iCloud. If you want to make a backup for your data on iPhone, proceed the operation to do.
4. When iCloud asks you whether to allow iCloud to use the location of your iPhone, just tap "OK" to turn it on.
5. Now you can see "Find My iPhone" appearing in Settings > iCloud.
6. If you've lost your iPhone, Find My iPhone can help you locate it. Go to Settings > iCloud and turn on the Find My iPhone feature. Turn on Send Last Location to send the last known location of your iPhone to Apple when the battery drains to a critical level.
If you've lost your iPhone, enter http://www.icloud.com, you can locate your iPhone.
Sign in your Apple ID, tap "Find My iPhone" and the system will send you're the location of your lost iPhone as long as your iPhone is on.
When you set up Find My iPhone, Activation Lock is turned on automatically. Activation Lock makes it harder for anyone to use or sell your iPhone, iPad, or iPod touch if it's ever lost or stolen.
I am sorry to hear that. If you can't find your iPhone back via Find My iPhone, you can try iPhone Data Recovery which can restore iphone data from icloud or restore iphone data from itunes backup.