// 383: Force the action subject to move to oMoveTo.
void ActionForceMoveToObject(object oMoveTo, int bRun=FALSE, float fRange=1.0f, float fTimeout=30.0f);
So something like this:
AssignCommand(oNPC, ActionForceMoveToObject(GetFirstPC(), 0, 1.0, 30.0));
You shouldn't have to use SetCommandable() as creatures are always set to commandable by default, and it doesn't affect movement anyway. All it affects is whether the character can queue actions; setting it to false is essentially stunning them without the stun effect. Since you haven't done that (I think) you can ignore it.