How to see who hasn't filled out a form

Can you describe your tables in their relationships? For example, example does one employee have many Weekly hours tracking forms?   

If that is the case, then you can make a summary field on that relationship to detect on the employee record if they have any form submitted in time.  Then you can have a Custom email Subscription go out a preset time of day and day of the week for any employees who have not submitted their form. 

This assumes that there is a user field on the employee record so that record knows their userid.  You can create a rpeort filtered when the employee is overdue in submitting and the employee userid is the current user.

Then you can send out that same report to all users and each employee will only receive the report if they are overdue.