I would try to involve them in new hobbies and interests that would increase their confidence.
Ask them what their dream is and try to help them to make it come true.
Love them unconditionally above all.
Absolutely. If a friend of mine had a self esteem deficit I would find an appropriate time to mention it to him/ her. I would want to help them understand why they did not feel good about themselves, and hopefully help them work towards better self esteem. I don't like my friends to be unhappy. Btw I am a licensed board certified professional.
the best way is to ask them whats wrong and if they tell you that its nothing tell them that you can see it in their eyes and that they shouldn't be sad that they look beautiful/girl better/guy when they smile
well try telling him that you were playing and that he has no right to listen to others.I had a friend that was really chubby and now he plays major league football and has girls falling for him everywhere.Your friend will be like that someday.But first he has to stop listing to them and he needs to listen to the true friends that he has.Every solution starts with a problem.For it to become a solution it needs to be fixed.
your welcome.Also tell him he needs a vacation sometimes.Everyone needs to have fun sooner or later.