Message icon is gone from my MarBookair

If you mean that it is no longer showing in your dock, then try this:

1. On the keyboard, hold down the "command" key while typing spacebar
2. In the Spotlight search box, start typing "messages". When Messages.app appears in the results, click it to launch Messages.
3. In the dock, right-click the Messages (green) icon, then choose "Options" > "Keep in Dock"