How to hide your online status on Facebook for one, several or all of your friends?
Step 1: Log in your account, click on the symbol Gear in the lower right corner and choose “Options”.
Step 2: Select “Turn off chat”.
Step 3: There are three options available for you. Choose the one from the contact list.
1. Turn off chat for all friends
2. Turn off chat for all friends except...
3. Turn off chat for only some friends...
Then select Okay to complete.