New Single Guy, from one single male to another the odds are not in your favor in finding a single female roommate. Showcat is right about going with an organized single group instead of trying to meet one lady to spend anywhere from 3 to 7 or more days on a ship.
Even if you are lucky to get a female travel mate there is a possibility you might not get along at the beginning or in the middle of the cruise which could ruin BOTH of your vacations.
But if you insist on a female travel companion do what Pat suggest and go to "Seeking a Cruise Companion" on this site where you can post. Mind you I have never seen a single female post wanting to room with a single male.
Last advice, it is better for you spend the extra dough to have a room to yourself just in case you do meet that single lady.