Nutritonal Supplements are a great addition to your muscle building plan but they are not magic bullets.  Supplements will not compensate for a poor diet and slack weight training efort.  If you find you are not making any gains your diet and training (or the lack of it) are the likely culprits. If your training and nutrition plans are sound nutritonal supplements can give you that extra boost.
BUT...
They are expensive and can empty your wallet real quick. Your money is most likely best spent on real food sources.
"Don’t be the best built pauper in town, build muscle and strength without breaking the bank"

Building Muscle Mass
The 2 factors that contribute to gaining weight and  muscle mass are Diet and Exercise. Both are equally important.

Gaining weight
You have just got to eat more calories than your body burns.
To work out how many additional calories you need to eat, men should multiply their body weight by 15.

Women should multiply their body weight by 12.
The result is the number of calories that you must consume each and every day while maintaining your existing level of activity. This will only maintain your existing body weight. To increase bodyweight eat an minimum of 500 EXTRA calories.