The Facebook app allows you to keep track of your friends with a location-based feature called Nearby Friends. This application allows to see where your friends are on a map. Here are the steps on how to set up Nearby Friends on your mobile.
Open the Facebook app and then tap on the Menu button to display the navigation drawer. Go to Favorites > Nearby friends:
Click on the drop down menu below Choose who can see your neighborhood or city and select with whom you want to share your this information (Friends, Friends except Acquaintances, Family, Close Friends...):
Once done, tap on the blue Turn On button to view your nearby friends:
How To Invite Your Friends to Join Nearby Friends
Tap on + INVITE FRIENDS displayed at the top right corner of your screen to invite other people to try out this feature.
How To Disable Nearby Friends for a Specific Friend
You can configure the Facebook app to automatically turn off location sharing with a contact after a number of hours. Go back to the Nearby Friends screen and then tap on the small arrow icon displayed next to desired contact. The Share your precise location with username until menu will appear. Choose one of the available presets and tap on Share:
N.B. This setting can be configured for each of your individual contacts.
How To Disable Nearby Friends for All Friends
Tap on the Cog button displayed at the top of the Nearby Friends screen and then toggle this feature off: