Referrals and Allies
Your Command Base Infrastructure level determines how many allies you can have. Each active ally gives you +1 to all 3 stats and lets you gain bonuses from surplus tech level 6 and higher equipment.
Referrals are people who've joined the game and entered your referral code (found on your profile). You can have any number of referrals and as each gains levels you gain experience.
Referrals can also act like allies giving you bonuses to stats and additional bonuses from surplus tech level 6 and higher equipment. Your Command Base Infrastructure also determines how many of these can be giving you a bonus at one time.
Note that referrals have their own limits - a referral never uses up an ally slot, and you cannot use an empty referral slot for an ally. If you can have 4 allies you can also have 4 referrals.
To get referrals you need to get your referral code out there - telling friends or putting on your Facebook page or on a forum. One way to do that is to add a review to the Zombie Moon game download page (open the http://www.zombiemoongame.com browser link with your device to automatically be redirected to the right app store page). New players read reviews before downloading and if you include your referral code in your review, they may use it.
Searching for players can be done within the BATTLE game area (and in Zombie Moon 3.0, within the new ALLIES SEARCH tab). Each player listed shows as active or infected - infected indicating the player has not played within the prior 2 weeks. Clicking a player listing will bring you to their profile which will provide you with a more exact time of last play and provide you the ally option.