Mix a rooting medium by combining one part peat moss and one part perlite by volume. Fill a pot with the rooting medium and water until it is moist but not boggy.
Cut a leaf from your hoya plant that includes a piece of the leaf's stem that is no more than 1 1/2 inches long. Push the stem end into the rooting medium and firm the medium around the stem so that it stands up. You can also sever a plantlet if your plant is old enough and push it into the medium in the same fashion.
Place a small pot in a plastic zip top bag. Cover a larger pot with a plastic dome or cover. Protect the plant cutting from bright light or harsh conditions while it is forming roots. Hasten root development by placing the plant on a seed-starting mat set 10 to 15 degrees higher than the ambient air temperature.
Watch for new plants to form at the base of the cutting. Remove the plastic covering once plantlets have formed. Cut the leaf-petiole cutting from the new plants and reuse it for starting more plants if you wish. Do not cut anything from plants started from plantlets.