If you suspect data loss the first requirement is to record any information you know about the missing or deleted virtual disk. Relevant data includes: virtual disk size, thick or thin provisioning, virtual machine name, guest file system and the type of data contained.
Next, reduce reads and writes to the affected datastore. If the datastore contains active, thin provisioned virtual machines, power them down as soon as possible. Whatever you do, don't migrate any active virtual machine (Storage vMotion or otherwise) to or from the affected datastore without first speaking to a data recovery professional. You may unwittingly increase the complexity of the VMware data recovery and could reduce the chances of retrieving the data.
In case of a VM with missing or deleted snapshots, don't power it on. And if the machine is currently running, power it down as soon as possible.