Question: how do you block someone from seeing you on messenger?
Answer: If you use Facebook Messenger for any reason, all of your friends who also use the service can tell when you're active. ... 
Next, tap the “Active” tab at the top.
Tap the toggle to the right of your name to disable your active status. ... 
Disable Active Status on Messenger.com. ... 
Next, click the “Active Contacts” setting.