Google’s voice-command system expands it reach in your phone further by adding support for some third-party messaging apps. Now, you can talk to the Google Now Launcher to send messages for you on WhatsApp, Viber, and WeChat. You just have to say: “Ok Google, send X message to Y: add message.” X represents the service and Y is the person in your contacts, that contact has to have the same name on your device and the corresponding app though for it to work. So, you can say “Ok Google, send Viber message to dad: Pick up milk today.” The app also adds support for Telegram and NextPlus for voice commands.
Source: SlashGear