This page of our Control guide contains a walkthrough for Old Friends - one of the side-quests found in the game.
To start the quest, talk to Arish in Central Executive.
Walkthrough: You need to get six pouches that belonged to Arish's men. Remus can be found in NSC Energy Converters.
Guy is in Atlas Chamber. He is accompanied by many opponents, so start with eliminating them.
Another sought character, Cho, is in Ventilation.
Hazzard is in Black Rock Processing. Wears heavy armor and uses a grenade launcher.
The final two enemies, Hepstonall and Thompson, are in Blackrock Quarry and NSC coolant pumps.
Arish will reward you with some modifications, crafting materials, and 4 skill points.