Most people who are excessively fun-oriented (with the exception of those who engage in extreme sports for the adrenaline and/or endorphin high) probably do so as a result of emotional problems, rather than addiction.
Fun is certainly mood-altering, but much depends on how one defines addiction. The most accepted definitions involve engaging in activities that cause trouble in daily life, but continuing to do them despite the consequences. There are also the issues of compulsion and withdrawal. One must also consider the definition of “fun.” If it always involved drinking or drugs, there could certainly be an addiction component.
We would add that there is nothing wrong with fun. It is one of the things that make life worth living. If, however, it has reached the point of making life more difficult, instead of making it happier and more carefree, there is certainly something to be looked at, no matter what we call it.