Alan Stein is one of the top strength and conditioning coaches in basketball, and he works with players your age who need to gain weight all the time. Here is an article he put together about nutrition with basketball players. It includes a recipes for a "Weight Gain Super Shake" that might be useful for you.
Other than that, eat a lot, hit the weight room hard and keep at it. Good luck!
Eat a lot, work out hard(dont overwork yourself) and make sure you are getting a lot of protein and creatine, you should beef up pretty quick, just stop when you feel you have packed on enough.
There is a huge difference between putting on weight and putting on good weight! I am no expert in this field and can not provide you good advice, I do suggest you get with a professional in this field:
Ryan, is our 3-Point Academy's Director of Sports Performance - he knows all that stuff: You should definitely talk to him or someone else in that field.
Founder of the worlds first ever online basketball camp, 3-Point Academy
Our home website; Innovative Athletes
The bottom line is EAT! Do you like to eat? It's also mentioned that you don't want to just put on weight, but, put on good weight. And, by that, we mean weight that your body will feel stronger, but, not sluggish and tired. When you eat, try and intake a little more on your carbs. Add a weight gaining shake loaded with protein in between meals and before you go to bed. Last, add weight training at least 3 times a week. Nothing heavy, but, enough to challenge and grow your muscles. Don't worry about your cardio if you're running ball at least 4 times a week.
Try some of that.