Are social networking(facebook,twitter etc) sites effective means of recruitment?

I want you to use google scholar mainly. And I want you to put all of the references for me to be able to look through again. this is going to be a draft version of literature review of my dissertation. I mainly want you to find a lot of articles about the usefulness of social networking sites on recruitment process. To search that if it is useful for people to find jobs, if it is helpful(not actually to get a job but to find it). In my dissertation I am going to talk about how is this different in the UK and in Azerbaijan. in the future I am gonna do a survey among people from both countries.And I am gonna upload 1-2 literature review samples as well.