I can't find one of my students in AP Potential.

There are a number of reasons why a student may not appear in AP Potential:

If the student didn't grid his or her grade level properly, he or she may not appear in the grade-specific roster you generate. Try generating a roster that includes "All Grades".
If your school's score reports were significantly delayed for any reason (including score holds), there is a chance that the data was not available to load into the system in time for the initial launch. Additional data will be loaded monthly to account for these delays.