How can I know who is viewing my Facebook profile?
I WANT TO KNOW WHO'S VIEWING MY FB
Facebook doesn't want to allow people to do this, and considers as a violation of their policies, so even if there is something that enables you to do this, Facebook will disable it.
If you see any link claiming it, Don't click it...report as spam, these are just traps to get your private info and harm you. stay safe.
There were apps that get access to ypur profile, and circulate their spam by making wall posts, creating events and inviting people.
There are some apps on fb that shoes who interacted with you the most, and rank them as fans.
From Facebook (Link)
"Facebook does not provide a functionality that enables you to track who is viewing your profile"