Have people wearing them. They say that word-of-mouth is the best kind of marketing. If you have genuinely good designs out and about you will get more business.

Besides that, you could try starting local by selling out of local stores or setting up your own mall kiosk or something small like that.

Besides that you could use just your own personal brand to spread your link around - i.e. Put the link on your facebook/myspace/aim profile/twitter and just everywhere you connect to others online.

FYI, youth shirts are a very populated market and I suggest that if you are steadfast about the idea that you start small and build brand strength locally instead of trying to spread thinly everywhere.