I'll address Fair's question.
If an I-9 is not completed, the employee cannot legally be permitted to work after three days, so the ramifications to the employee are loss of wages/employment.
If an I-9 is not completed, there are no ramifications to the employer UNLESS they are audited by the USCIS, in which case the employer will probably receive a fine. The amount of the fine will be determined by the extent of the violation.
There is no financial benefit to the employee, to report the employer's failure to provide an I-9 form.
If a W-4 is not completed, the only ramification to either employee or employer is if the employee requests a form, is not provided one, and the employee wishes other deductions than those being taken by the employer. In that case, the employer will be liable if reported to the IRS.
With regards to state tax forms, see above.