As a young dancer, I faced the same situation and as the only boy taking ballet in my hometown, had nobody to turn to.  So, don't feel like you are the only guy to have to deal with this question.  "Dr. Dancebelt" was created to help beginning male dancers with this and similar dancewear issues.

First of all, at age 13 you should definitely be wearing a dance belt under your tights.  Actually you should wear one for dance even if you don't wear tights.  They are the best protection you can get to avoid hurting yourself doing some of the movements peculiar to ballet (for example -5th position, beats, and sautes changement).   Dance belts were created to form a smooth bulge under tights with no visible lines, while keeping your testicles up and away from the danger of being crushed or bruised between your legs.  A secondary benefit is their ability to hide any visible evidence of an erection, which could be extremely embarrassing in class or performance.

Whether you buy a thong dance belt or one with a full seat is up to you, but I am not a fan of the full bottom model.  I guess if you had hemorrhoids or something, you'd want to go that route, but the traditional thong style is the best and most popular for several reasons.  -They are invisible under tights and don't show any underwear lines.  -They don't cover your butt, so the gluteus and hamstring muscles aren't restricted or inhibited from working to full length.  -They are the most secure.  Since a thong style doesn't cross or cover any muscles it will always stay in place with a constant tension no matter how you move. You won't find yourself off in the corner making mid-class "readjustments" or trying to pull down a full coverage seat that has climbed halfway up your butt.   -If you find yourself performing in white tights someday, you'll need to wear a thong style dance belt, so you might as well get used to the feel.

The thought of wearing a thong is scarier than the reality, although they do take a bit of getting used to.  Dance belts are supposed to worn tight enough to prevent anything from shifting around inside them.  You’ve probably never worn anything else even half as tight as a dance belt, but you'll find a well fitting one is actually quite comfortable - and certainly secure - once you get used to the unusual feel.  You will come to appreciate your ability to let loose, jumping and leaping around with wild abandon, knowing there won't be that painful bounce when you land.

Some recommendations:-CAPEZIO model 26: plain cotton/lycra model is secure and the easiest to find.  The cotton is also a good sweat absorber.  My daily choice.-MSTEVENS model 007: a sleek looking lycra model is considered by some the most comfortable dance belt available, although the thong is too narrow for my taste.  Also it isn't as supportive as a Capezio.  Sized very small, so go up one size from what you think you need.-CAPEZIO model 5930: quilted pouch to round out the bulge lines.  Considered by many professional dancers to be the cadillac of dance belts especially for performing.  It offers an extra secure fit, but extremely wide elastic waistband is not covered by fabric and is pretty industrial looking. Dance belts are measured by waist size.  Although most dance stores don't carry an extensive selection of men's dancewear, most have a small selection of men's tights and dance belts stashed away somewhere.  You'll probably have to ask the clerk where they hide the men's gear.  You can also shop online if you live in a town too small to have a dance store, but be prepared for delays and perhaps incorrect sizing if you go that route.   Some online stores that carry dance belts:DiscountDance.com  Tutu.com  RiversEdgeDancewear.com The best color dance belt to buy is flesh colored.  The same dance belt can then be worn under black practice tights or white performance tights.  A flesh colored dance belt is more invisible under white tights than a white one, in the same way a white T-shirt under a white dress shirt becomes a "super white" look brighter than a single white layer.

When putting on a dance belt it's important to take the time to get all your parts placed where you want them, as comfortably as possible, because once it's on, nothing is supposed to move until you take it off.  Sometimes, there will be internal slippage inside a dance belt as you move through class, but this indicates a bad fit.  You may have to try different brands and sizes to find the one that works best for you.

To put one on, pull your dance belt up around your waist or hips, to the height you normally wear your pants.  Do not try to cheat by wearing it low, hoping to avoid thong tension.  Your penis is supposed to end up facing up towards your belly button, so you can get that process started by letting the dance belt catch it as you pull it on.

Next, reach inside the dance belt and pull your scrotum up inside the pouch.  Your testicles need to be up and front, well clear of their usual dangling position.  Adjust your penis position to face straight up.  Then, make sure the pouch isn't riding too far up by pulling the pouch's bottom back down and  back.  Make sure the thong is firmly seated between your butt cheeks, pulling any looseness towards the rear waistband.  Again, don't attempt to cheat by letting the thong float loosely.  It's going to end up as far up your crack as possible halfway through class, so you should place it where you want it to go rather than leave its comfort to chance.

It's almost a tradition for male dancers to complain about dance belts, but they wear them voluntarily, knowing their male parts are safe and secure, and their line smooth.  

If you have additional questions, feel free to write again.  Good luck with your dancing! Doctor Dancebelt