In short, I'd say yes.

However it depends on the situation, and mostly on the Facebook group it self.

In example, if I'm making a research on the perceptions of road safety in a Town, and there is already existing a Facebook group called 'Road Safety in Town' and it is safe to presume that the group is a good representation of the people living in the Town. So I would use this group for data. I even might make the whole research based on this group. But if the group name is 'Formula 1', I would not, even though they are talking about safety and vehicles.

But if the Facebook group is brand new, established only for the purpose of the research, now it is tricky. The problem comes from the way Facebook groups are spread - friend's invitation, mainly. So it would be mainly my friends that would be members, therefore it would be biased. So I would use this group only as a consultation tool, to have an extra critical thinking regarding my research.

...you understand my point.

Thank you Bojan Rantasa, Basically, I am working on research topic of E-business deployment, I already clarified my main tools and methods that will be used for data collection. But, I noted that there are significant Key people in Facebook group who I know personally, and they has been experienced some aspect and practices of of e-business deployment among universities

Therefore, I am wondering whither their feedback could add value to the collected data.  However, I agree with you that their feedback gained me a positive  support and introduce me to key issues and persons from the Case study field. 

Do you think adding this kind of action to my research activities report could give a positive and add value to the report contexts!!.

I think you should ask your self the question "Where can you acknowledge the input provided by this Facebook group in your report?"