How to find Facebook ID?

In order to use our Facebook ID Finder, you don't have to be logged in to your Facebook account. All you need to do is enter your Facebook Profile username or Page in the top input field, and in a second you will find all the information you need.

For example- 

http://www.facebook.com/Google
here Google is our user name so just type Google in box and find ID
we have got ID Code - 104958162837
Now to tag it you have to write- @[104958162837:o]
Hope you understood.