I was having the issue earlier to, and I had nearly every solution posted on every forum. Then my brain started working and something clicked. Did you make sure you have bonjour running? Because I didn't i had turned mine off in system settings. I only know how to do it on microsfot not on mac so the process i followed was
Start-->MSCONFIG(just type it in the search bar)-->then click the tab SERVICES-->
I hide all the microsoft things with the little box at the bottom left of that screen, and my apple services boxes where mostly unclicked, i made sure all of them where clicked, espcially the bonjour sevice, and then clicked ok, restarted my computer, and opened itunes and now my phones show up
Another thing to try -- ensure you have IPv6 enabled on your Mac.
None of my devices were syncing, then I went to:
System Preferences > Network > Wi-Fi > Advanced > TCP/IP > Configure IPv6
-- set to "Automatically" (or in my case, I use "Link-local only")
Then in my case, voila - both my iPad and iPhone were syncing.
I now have Yosemite on my computer and ios 8.1 on my phone. I couldn't get my iphone to show up in the top left hand corner when I turned on itunes. I had to sync over usb for a little bit. I didn't know why my Iphone was not recognized. I knew my computer knew my iphone was there because I could still send and receive texts on my computer. I double checked to see if both devices were on the same wifi. They were. I finally found a solution. I turned off my iphone and turned it back on. When I did that, Itunes finally recognized my Iphone over wifi. I don't know why that worked but it did. If you can't get itunes to see your device, try restarting. It might be as easy as that.