Awesome!! It worked for me.
I was struggling for a month to get this missing AirPlay icon fixed in both my iPad (ios 7 and 8) and Macbook Pro (Yosemite). I always assumed the problem was with my Denon AVR-X1000 or something to do with my Macbook Pro and iPad settings. I tried every possible combination only to fail in vain. Finally I chucked the AirPlay option and ordered a Logitech Bluetooth receiver adapter and plugged it to my AV receiver's RCA/AUX inputs, only to find that the sound quality was absolutely pathetic. I then realized this was happening because lossy compression of the bluetooth protocol and I didn't want any quality loss in my music. So, I fell back to the AirPlay option.
I tried googling around for the solution for a whole day and tried out everything people said and finally I tried a "AirPlay missing icon + TPLink" search in google and voila it landed me in here. Never thought a simple security setting was causing the issue. Before this suggestion I set my routers in dual mode AES+TKIP in my previous setting which was the cause of all the issue. Following your suggestion I changed the security to WPA2 with AES mode and voila the problem got solved.
Note: Dual mode of TKIP + AES will also make the AirPlay icon missing/disappear. Did not try but pure TKIP also may not work. Set your settings only to WPA2 + AES to ensure you have your AirPlay icon visible in your Apple devices or laptops.
Thanks a lot Alex!!