They are easy to find at the moment because they simply are large and close to their star. This means that their gravity causes the Star to wooble quite a bit because their centre of gravity is pulled a bit closer to the planet than it would be otherwise. Since both the planet and star both orbit the centre of gravity of the system, this causes the star to appear to "wooble" and it is this wooble that is what is looked for in the current search for exo-planets so that is what is found.