Hi,
Only users who are able to sign in to your Apple ID online at icloud.com/find and by using the Find My app on a device currently signed into iCloud Settings can play a sound on the device.
Note: If you are apart of Family Sharing, members tied to the FS will also have the ability to play a sound for that device.
iCloud.com/find will first require entering the two-factor verification code sent to your trusted phone number, prior to allowing a user to sign in and play a sound.
If you feel as if your Apple ID account is being accessed by someone else, I would recommend changing your Apple ID password. This should resolve your issue.
Hope this helps.