There's a page on the site that lists all the comics. I'm not sure if it's on the mobile app or if it's easy to find, but here's the link to that page.
http://tapastic.com/browse/list
As far as updates, it's really on the artists to come up with a schedule and maintain it. I feel your pain, I know some good ones that have gone on extended hiatuses. :.(
There's a forum post here, were we've been kind of indexing our comics and we say how often we post, maybe that'll help?