Answer:
Social Network Theory, is a theory that arose in the 1960´s and which began to explain an alternative viewpoint to how people related to each other, not on the basis of their individual characteristics, but rather, on the relationships they formed, and what was brought into that relationship. It has been characterized because it is always diagramed as a series of points (individuals), and connecting lines between them (relationships).
Social Network Theory is used to explain the appearance of certain mass behaviors in people, and trends, even if individually, the person does not display a specific characteristic that would explain the behavior.
In the case of smoking, especially in teenagers, this theory applies perfectly, as it is known that teenagers, as they are still in the process of forming their own identity, tend to depend on social networking, and especially, the acceptance by peers. This means, usually, that they will adapt to whatever the social group where they are is doing, in order to form a positive relationship with the others, and feel a part of it. This means, that even if personally the teenagers in the group did not have specific characteristics that would explain why they took smoking as an activity, they still did it because it was the social behavior of the group, and this activity strengthened the relationship among the members of the group.