Airplay icon disappeared after upgrading to IOS 6 with Verizon Router.
After upgrading to IOS 6, the Airplay icon was missing and couldn't use my home Pioneer receiver. After talking to tech support, the Airplay devices simply advertise themselves over the network. Traced it to my Verizon FIOS MI424WR router. Airplay started working again when you disable "IPMG Proxy" which is enabled by default. Login to the router, Advanced -> Yes -> IPMG Proxy - Set IGMP Proxy (Enable/Disable): to Disable and save. Hopefully this saves someone a headache.
iPhone 5, iOS 6