Diego,
I had the same issue as you. Here’s how I solved it and why it happens: As Kelly said, attendees will not show up on the list unless the relevant order is makred as “complete”, so you have 2 options.
1: Manually set orders to complete whne that is so.
2. If, like me, you need a way to set orders as complete automatically, that is more of a WooCommerce issue than a WooTickets issue. To that end, I offer this solution: http://docs.woothemes.com/document/automatically-complete-orders/
Hope that helps!