Moto G does not support Miracast (wireless display). Please note, the cast screen button is for Chromecast and only works on Nexus devices.
But you can use Chromecast to mirror (cast) phone screen to TV (you need also install the Chromecast app, in addition to get the Chromecast dongle). http://allaboutchromecast.com/android-screen-casting-for-chromecast-is-now-supported-on-all-android-devices-with-kitkat-4-4-2-or-later/
