The Facebook Messenger app allows you to add contacts to your list of Favorites, which pins people with whom you chat the most to the top of your contact list. This walkthrough works for the various versions of the Facebook Messenger mobile app, including iOS, Android, and Windows Phone.
Open the Facebook Messenger app. Click Menu > Edit (next to People with Messenger):
Tap Pin people:
Tap the + to add a contact to your favorites:
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