I own a Lumia 625. When I am not using the Facebook Messenger app its running in the background. However it doesn't show me as online to my contacts. What should I do?
It might not show online because the app isn't running in foreground. I mean you're not using it at the time. But, your friends should see a messenger sign(a bolt sign) to show that you are using messenger and, so, will be notified when they send a message. And basically you get notified because the app is running in background. So, you might not be shown as online, but as available to get notified about messages.