I have this app setup on my phone. If I were to loose my phone - would I go online to find out where it is?
Also, I am getting my son an iPhone - he has his own email /password for apple - how would I be able to track where his phone is if needed? Can I locate him by using the findmyiphone app on my phone if we have different accounts?
If you have different accounts, you will have to use the Find My Friends app (free) to locate your sons phone.
My whole family uses 1 iTunes account, mainly so we can share music and apps (no need to buy things more than once) so we can use find my phone.
I'm sure there's a way to log into find my phone from a computer, but what i do if I want to find my phone is log in from someone (anyone's!) else's iphone/ipad with my iTunes account. From there, I can track where it is on a map, or even send a loud beeping sound (handy if it's lost in the house!)
If it is truly missing, I can send a note that will appear on the lock screen, "this belongs to "descovy" call me at xxx-xxxx.
And if I really think it's stolen, I can wipe all my personal info off the phone.
My daughter once left her iphone at school. I checked in that evening and noticed it was moving up the freeway

I set off the loud alarm, and left a message to call me. I just kept setting off that stupid alarm every 5 min while I watched it move up the freeway. Shortly I got a phone call. The guy said he was the husband of the school janitor, and she had taken it home for "safekeeping" and would leave it in the office that morning. I thanked him profusely "what else could I do? Sure enough, 6am the phone returned to the school.
The app can't protect you from a smooth criminal, but it may be enough to detract a petty theft, or help a Good Samaritan help you out!
I work in the cash office at Target. When an iphone is turned in, the first thing I look for is a message from the owner. If you leave me a number I can call you! It's worked several times over!