In my research I've found three variations:
Wifi and Bluetooth never worked - To me this seems like a defective board or image on your sd. Try retropie 4 and/or NOOBS (full image) to install rasparian. If that doesnt work its probably the hardware. From what I gather both wifi and bluetooth functions are on the same chip. For me, my bluetooth seems like its working, but I dont have any controllers worth testing. I got some fake ps3 controllers but I think its those that arent working and not the bluetooth. in rasparian the bluetooth icon was lit and said no bluetooth devices found.
wlan0 is listed in 'iwconfig' - This seems to be the best scenario of the three. If its listed it seems like people have been 50/50 in getting it fixed. Some say that apt-get update /upgrade fixed it, or various other updates. Or reflashing the sd card. This doesnt seem to transcend os installations.
wlan0 isnt listed in 'iwconfig' - This is the boat Im in. I know wifi worked at one point in time. Maybe it the chip fried, or maybe there is something wrong with the firmware or other bios/drivers stored directly on the pie. Updating the firmware didnt help, and no other command or config change works. This transcends all OS installations so in one way that limits the search and is good. But its mostly bad because the fix for the others may simply be to reflash your sd card.
Good Luck, Im still messing with mine hooked up to ethernet, but in a week when Im satisfied with everything except wifi ill be returning it for one that is working. I know one other poster took this route. Anyway, decide what group your in and narrow your searches. If your in my group let me know, I have 4 different threads out there, unfortunately none have the answer. Mine seems to be the rarest and most unresolved, but maybe I just think Im special.