Mark Granovetter described in his publication (1973) "The Strength of Weak Ties" how social constructs can be distinguished in two strong (family, friends) and weak (acquitances) ties. Those ties play a significant role when it comes to helping each other out, e.g. finding a job.
Social Theory, Volume 1 (1983) chapter 7 reviews the above mentioned paper and adds empirical information:
PDF"Weak ties provide people with access to information and resources beyond those available in their own social circle; but strong ties have greater motivation to be of
assistance and are typically more easily available. I believe that these two facts do much to explain when strong ties play their unique role." (P. 209)