If you have been griefed and there are no mods online you can check who griefed you by yourself. This would make life of the mods and admins easier instead of getting a lot of mod requests. So to check who griefed you, you will need a wooden pick and a couple of dirt blocks (or any other block).
Step 1. If someone stole block(s) from your house place a dirt block (or any other block) where the block(s) used to be.
Step 2. Get your wooden pick and then right click the block you just placed.
Step 3. A record should pop up saying who stole the block. You will know who the culprit is by seeing your name and someone else's name you do not recognize. That person is usually the griefer. Also make sure you take a photo of the record so that you have proof.
Step 4. Report the person on the forums and upload the photo so that a mod or admin can punish the griefer
If somehow your contents of a chest got griefed you can just right click the chest with a wooden pick and it will show a list of names of who accessed the chests or modified it.
So this is how to check for griefers. Thanks.
-qwerty