Ft. Lauderdale is a place to start. if you're young and have a neat appearance, you can possibly find work on a yacht.
now, being as specific as you are to go to Europe might be doable, but only certain times of year.
Antibes, France is the destination of many yachts in the winter months.
you'd be required to take a course in safety before you were hired and at your expense. there are schools in Ft. Lauderdale that cater to yacht crew training.
many people get their start in yachting doing day work on the yachts. a place to start would be here:
http://www.tripadvisor.com/Hotel_Review ... orida.html
the neptune group is a better place by far, but initially more expensive. one better thing about them is that they will refund you the difference of what you paid if you get a job on a yacht and need to leave on short notice.
Floyd's Hostel is rowdier and not as clean or nice. there are other crew hostels in the same vicinity, varying in price and quality.
don't know about your funds, but being in a crew hostel as opposed to living on the streets or somewhere else will get your foot in the door on a yacht crew much faster.
the only downside to getting on a yacht is that many don't want Americans.
they prefer Aussies, Kiwis and South Africans, but some will hire you if you've got a pleasant personality. that BTW, is a must....working around rich people you'll have to be, whether you like it or not
hope this helps.
All mankind is divided into three classes: those that are immovable, those that are movable, and those that move.