User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-24501441-20140203223354/@comment-1359322-20140204005523

Actually it's a matter of the formality of the honorific. For starters, most people don't allow anyone to simply use their first name. They only allow close friends and family to use their first name.

Back to the honorifics, it's like i said, it's a matter of formality, "-san" (さん) is considered as a formal way of addressing someone and is a title of respect typically used between equals of any age, while "-kun"(君) is considered a more informal way of addressing someone and is used by persons of senior status in addressing or referring to those of junior status. Also "-kun" is more commonly used by male but it's also applicable to female.

As for "-chan"(ちゃん), it's a form of honorific where it's used for expressing that the speaker finds a person endearing and close. In other words, someone they care about and get along well with, could be family or very close friends.

"-Sama"(様) is a more respectful version of "-san". It is used mainly to refer to people much higher in rank than oneself, for example, toward one's guests or customers. Then there's also the "-shi" (氏), a formal honorific used when writing letter and "-dono" (殿), which is somewhat in between "-san" and "-sama" in level of respect.