We have simulated the structure and aggregation kinetics of sodium dodecyl sulfate (SDS) and dodecane (C12) on a graphite surface in the presence of point and line defects. We find that while vacancies do not affect the orientational bias of the molecules, they interfere with aggregate formation. Specifically, they disrupt the formation of extended aggregates. Line defects in the form of surface steps, on the other hand, tend to localize the aggregates in their vicinity and induce specific orientations along the step edges. We demonstrate that this orientational bias can be tuned by manipulating the terrace widths. These results suggest that extended defects could be employed to localize and orient surfactant aggregates on the basal plane of graphite, thus providing a means to create patterned aggregate domains.