thanks for reply,
for ex., I want to know their interests , activities, for period of time,so I can make clusters .
i.e I want to find similarities between them depending on what they are doing over time.

I want study on group of authors.
just need know what is the first step?

regarding what you suggested , do you mean I have to participate in one of the groups you mentioned.
I have account in facebook, is this enough to get information?
your reply is very appreciated