Snowball sampling is the sampling procedure used for this particular study.
Explanation:
In the initial stage of snowball sampling, individuals are discovered and may or may not be selected through probability methods.This group is then used to refer the researcher to others who possess similar characteristics and who, in turn, identify others.
It is also especially appropriate for some qualitative studies. Snowball sampling sampling uses a referral approach to reach particularly respondents who are difficult to identify and contact.