I have not done the preditor class quest in Freeport, but in Qeynos, it takes place in an instanced zone within a zone. This is a mini-zone that only you are in... it is created just for you.
Since you know the general area you need to search, you could wander around right clicking on all the doors around there and when you find one that says "enter Seafury Buccaneers' den" or something like that, you'll know you found the right spot!