Click the "Search by Type" button in the upper right corner. That opens up more options that include a filter for "posts by" or "threads started by" user.

It's still not quite working, though. Here's the search results for all threads started by me: http://www.cartographersguild.com/se...searchid=14908

I know I've started more than 12 threads here, but still only one of my tutorials shows up. It's closer than it was, though.