An iPad that has been instructed to play a sound (or erase) using Apple’s Find My service will only do so when it receives the command to do so - this, logically, being determined by the iPad having an active network connection. If the Find My service indicates that play a sound or erase is pending, then the command has not [yet] been successfully delivered to the iPad; the status will change when [if] the command is successfully delivered to the device.
While the Find My service might be showing a location for your missing iPad, this does not suggest that your iPad is connected to a network...
Your iPad/iPhone will use its low power BTLE radio to periodically broadcast a "beacon" signal - which can be detected by other Apple devices that participate within Apple's Find My network. Receipt of the unique beacon signal is anonymously transmitted to Apple's servers, by the receiving device - along with the location of the device that received the beacon signal (this typically being within 30' (10m) of the device that transmitted the beacon signal). This mechanism uses millions of Apple devices as a network of remote sensors - but is not two-way.