You go on all topics and then your favourites, I think.
As far as I know, with the clusterfuck that is Bungle.net, you can't. Unless you want to spend hours wading through the dropdown menu that has no end in sight to your posts which are probably in the year's worth in number.
Go to Google. Search site:www.bungie.net whatever was your thread title.There is no step 3.....Profit.
Go to your "Activity" tab on the right of your main profile page and search manually. 'tis the only way
It's one of those things Bungie fucked up in the update, you'll have to dig through unless you had a unique tag for your threads