I got a friend request from someone already a friend on my account. This is not a sign their account was hacked but just someone pretending to be my friend. If you want to help your friend by reporting the fake account to Facebook, here is what you do.
On the Friend request, click on the profile name listed.
If you are not sure if they are on your friend list or not in the Search Facebook box, top left-hand corner of your page, type in the name in question. Facebook will give a list of possible matches and you'll notice the word Friend under their name if you have them already added.
Going to the fake profile from the friend request by clicking on the name in the friend request box. You'll go to that profile. A fake profile more likely will contain no posts and very few friends. Go into their real profile from your search and you'll see the difference.
If you want to help your friend out by reporting the fake account click on the three dots just under the profile picture to the right. In the menu that drops down click on “Find support or report”.
In the next box to open, click on “Pretending to be someone”.
In the next box, in my case, I select “A friend”. If you are doing this for yourself then click "Me".
Then you'll be asked to type the name of the friend in question. A list of potential matches will pop down so click on your friends account.
Once the name is filled in click on the “Send” button.
Then in the next box click on the Submit button.
Next box click on “Next”.
Then a box of more options. You can block the fake account, hide it. Then click on “Done”.
Here is a copy of the email I received from Facebook.
You've now done all you can do.
Keep in mind this is not an hacked account but someone pretending to be your friend. If you don't want to report just delete the friend request and spread the word that there is someone pretending to be you or your friend online.