There are twenty surivors to be rescued in this DLC, five in each zone. The survivors are available right from the start if you choose, although you may find it beneficial to get them whilst doing the other collectibles when you are waiting for Nelson. Be warned, if a survivor dies he will not respawn making it not possible to get this achievement. The survivors are marked on your map when you get close by a little person icon.
The survivors are :
South Almuda - Jack,Mila, Maia, Vicki & Ryan
Central - Madeline, Bob, Sam, Alec & Jordan
Sunset Hills - Eva, Greta, Alex, Jasmine & Tracey
Ingleton - Steven, Kristen, Mike, Scott and Kaliyan
Here is a video guide showing you all twenty locations.
I completed the story rescuing all surviours at the end but achevement didn't pop. is it the surviours at the end of the game or the surviours you have to save from killing the zombies around them. Please anyone help its my last achievement.