To be accurate and correct:
You can grow Hops from seeds - and there is a vendor on ebay who sells them - however in most cases you wont know the type of hop.
The most common method is to buy rhizomes in March April which also guarantees the variety you will get. Vegetative propagation is used for many crops and fruit , and hops are amongst those.
Hop Rhizomes - are a woody runner - sometimes hairy (mini roots) with growth nodes spaced about 3-6" apart that is created near the surface and are different from normal roots , which in Hops look like thin brown carrots and have no nodes.
For advanced gardeners, soft wood cuttings can be taken now in the spring and be rooted under controlled conditions.
Lastly hardwood cuttings can be taken in the fall and grown on for next season, which I have successfully done over this last winter
Last comment about seeds, 99% of hops grown today are grown in the absence of Male Plants - ie all we get are Female, and this means we get no seeds in the cones. Seeds affect the flavor and texture of hop cones, thus the reason to exclude them.