Has anyone used partsim and if they have, where is the potentiometer?
There is no potentiometer in partsim.  

Why not just use two resistors and change the resistance as required?  

Partsim is a simulator rather than a schematic package, so using the resistance values rather than an adjustable potentiometer should be fine, (to my knowledge tracks are not simulated).

Same again for the switch, just build two circuits, one switch and one unswitched, (again to my knowledge the sim does not model switching transients).

Alternatively, email digikey and ask them to generate a potentiometer for the sim, (support@partsim.com.)