I would like to know if someone started working one week ago and you have their ssn can you access where they work... can you find out that quickly. Or do you have to wait until a pay period, a month, two weeks?

No, there is no cross reference at all till the company pays taxes they collect to the IRS, and even then, there is no real access to those records.

You may have to merely find where they work by having them followed, or court order to disclose where they work