You can join AACT (Against Animal Cruelty Tasmania) but I think there's a membership fee and possibly an age limit. There's not much activism here, unfortunately.
I just joined AACT and they do a heap of stuff down here (although a lot of it is in the North). They've told me they run a stall at the Salamanca Markets every month, and it's actually there next saturday which I'm going down to so I can meet them properly.
It's $20 p/y to join. I'm not aware of any age restrictions, but that may be because I'm over 18 so I might have skipped any info relating to 'minors'.
I emailed Animals Australia two weeks or so ago asking about events in Tassie, at that point in time they said that they had nothing coming up, but had plans for events in the near future.
Sooo today I went to Salamanca markets and did a few hours on the AACT stall there. Really fun bunch of people to be around. Had a chat to Neon (who is on the committee and very funny) about age restrictions etc. There are none, in fact they are hoping to get more youth into the fold.
Neon was more than happy for me to give out his e-mail if you would like to talk to him directly about joining up and helping out -