identifying devices using find my phone app I will try to be specific.
- I did receive this e mail:

Dear XXXXX, 
    Your Apple ID (XXXXXXX) was used to sign in to the Find My iPhone app on a new device. 
    Date and Time: October 6, 2014, 3:39 AM PDT 
Device: iPhone 5s 
    If you recently signed in to the Find My iPhone app, you can disregard this email. 
    If you have not signed in to Find My iPhone recently or you believe someone may have accessed your account, go to My Apple ID (https://appleid.apple.com) and change your password as soon as possible.
    Apple Support 


I am not the possessor of the quoted device, though the apple id + password are the right one
this means someone else entered my find my phone app using my credentials to track me (probably boy friend!!)


(i did already change my password, of course and already asked the apple care and they told me there's no way to track the device..)

can I somehow track (identify) the possessor of the device used to enter my apple id app?
In general, no. Apple won’t tell a consumer about another consumer’s details.

If you followed the advice of the email and changed your password after the time of the alert, then you have done what you need to secure your privacy.

In the past, Apple didn't send those emails and there was no easy way to know if someone had gotten a hold of your AppleID and your password for the ID.

It could be someone who is trying common passwords and stumbled across your account by chance to use it for fake reviews on the app store or it could be someone who you know and they guessed or were provided the password when you trusted them.

There's no way you can track things unless you were to get a law enforcement order sent to Apple's legal department and even then, you might not be able to get a satisfactory answer as to who accessed your account. That or a lawyer contacting Apple is the best way to get information about who may have your property to your credentials.