Thank you for posting in the Apple Support Communities. It sounds like you have enabled Find My Mac on your MacBook Air, but when you go to check it on www.iCloud.com, it says your MacBook Air is offline. There are a few things that you will need to look at if you are being told your MacBook Air is offline:
"No location available," "Offline," or "Location Services Off" alerts
This can occur if:
- The date on your device is incorrect.
- Your iPad (Wi-Fi only), iPod Touch, or Mac is currently off or not connected to a Wi-Fi network.
- Location Services is not enabled on your iPhone, iPad, or iPod Touch in Settings or on your Mac in Date & Time preferences. Learn more about Location Services on your Mac with OS X Lion or OS X Mountain Lion.
- You are located in a country where Apple does not offer this feature. This feature may not be available in all countries due to technical limitations or local law.
You can find the full article and more troubleshooting steps here: