MY IPAD AIR WI-FI 16GB SPACE GRAY GOT STOLEN BUT I ONLY HAVE A SERIAL NUMBER IN THE BOX,HOW CAN I LOCK IT OR FOUND IT PLEASE?

If you turned on Settings > iCloud > Find My iPad before it was stolen you can use the steps under "If Find My iPhone is enabled on your missing device" in the following link: If your iPhone, iPad, user iPod touch is lost or stolen - Apple Support

If you had not turned on Find My iPad before it was lost, there isn't a way to locate it. There are some suggestions in the "If Find My iPhone isn't enabled" section near the bottom regarding changing passwords and other steps.