Did you give a Google Form but want to know who still needs to fill out the Form?
You first need a Google Form that collects email addresses!!!!
You then need to add a sheet to the Google Form spreadsheet responses.
Scheduler by Alice Keeler
Coming soon is a stand alone Add-on to determine who did NOT fill out the form. For now, use the "Find Missing" feature in the Scheduler Add-on.
You want to be looking at the sheet with the roster. It will automatically compare the roster against the form submissions.