How to manually add a device to find my iPhone app?

I have two iPhones (one for me and one for my mom) and she has the find my iPhone app. My iPhone is stolen but that stolen iPhone does not have find my iPhone enabled (or installed for that matter).It has a lot of valuable data and information (passwords, email, etc.). I have that stolen iPhone's IMEI number (if it helps).So is there anyway to manually add a device to find my iPhone app? If not, is there any other solution I could do to find it?

Are they iPhone 4S or 5? You can use Siri to locate where a number is… Like on the TV advert.