I just reinstalled one of my machines with Fedora 21. The install went great, but when the machine was done rebooting, and I was trying to set up my access to a wireless network with nmcli (NetworkManager), I got the following error-message:
# nmcli dev DEVICE TYPE STATE CONNECTION enp0s25 ethernet unavailable -- lo loopback unmanaged -- wlo1 wifi unmanaged --
..and:
# nmcli dev wifi rescan Error: No Wi-Fi device found.
Spending a lot of time finding what the problem was, I finally found the solution. It seems that Wi-Fi support in NetworkManager has been separated to a plugin. The package NetworkManager-wifi was missing. So install it, reboot your machine and give it a whirl again. It should (hopefully) be working.