A social networking site has created a lot of issues where individuals are spending so much time on it and they are replacing the traditional communication. We can observe that people are on their smartphones while having coffee with friends, having dinner with families, out on a date with spouse and many more. Due to social network sites, people seems to behave differently when they go online thus in reality they may be quiet and timid. This research is to examine the pattern of individuals’ behavior and personality, the practice of self disclosure and addiction to Facebook. The researcher used a qualitative method and interview the selected informants. A purposive sampling is utilized in this study as the informants are an active user of Facebook. The researcher conducted an in-depth interview to find out the behavior from each informant. Five informants were evaluated and all of them have met the criteria of behavior and personality, self-disclosure and addiction. The researcher has applied the Five-Factor Model in the personality and behavior and the Five Factor internet addiction symptoms in the findings. The results of the findings showed that young adults commonly display consistent with personality and behavior, self-disclosure and addiction on Facebook, and the informants reacted to such behavior of self-disclosure because they are lonely, narcissism, emotional and low self-esteem. They also look up onto Facebook as a medium to express what they feel among friends for attention.