Where is my dog ?
If you know the gender of the dog, you use he or she, but if you dont know the gender you use it.
This should be the same with an individual or a person.
If you dont "know" (or dont want to know so as to be gender neutral) the gender of a person, you would need to use "it".
Where is this person ?
It is in his car.
But... this is awful because doing this can be understand that you consider the person to be an object (and it is degrading).
So
you have to use "they" or "them" instead of "it" (you can use "it" for animals, nobody care, curently... but the owner of the dog would appreciate you use something else than "it", be creativ).