Hello! I'm sorry to hear about your lost iPad.
You'll want to start by signing into iCloud.com. Once signed in, click "Find iPhone" (even though this isn't an iPhone) and then, at the top of the next screen, use the dropdown menu to select the device in question. Once selected, you'll be presented with a few action options -- two of these may be applicable.
I hope that helps! Please let me know if you have any additional questions.