Lost Within

On top of the ship where you get the quest from is a hatch. Enter the hatch, you can turn left for loot or straight ahead through the fire, into the next room, for the first missing person. He should be in the little alcove with the green light and the white box. Grab the key.
There is a chance he's not there. This was bugged for me as at launch of the DLC. Just log off and back on again. It worked for me. Others are saying you can exit and put some distance from the area and try again.

The next key for the pentashield is above you. Back out to the room with the burning engine and jump/climb up. In the far corner is the next key and the 2nd missing person. Again it was bugged for me. Log out or exit and go some distance away. When you get back in, hopefully you'll see the next survivor.
Back past the first man and through the last pentashield should be the last missing person at the end of the room.

Hope it helps.