I have the same problem like you. I am 18 years old, 180 cm and 60kg. Quite skinny and Yeah! I know the visible parts of the body.

But....I know it is possible to gain weight,. Although, I want to start my gain weight program but it is not my priorities right now. I love my body as it is for now.

So, here's the deal :- You need to have - Time, discipline, motivation and MONEY! If you think you have all that, then go to the link below and follow the comprehensive guide,

http://www.gain-weight-muscle-fast.com/

Just remember to put in an effort and if it still doesn't work. Consider visiting nutritionist and personal trainer to help you specifically. All the best and good luck!