I'd like to share a fun sourcing technique with you: using phrases for sourcing and Internet research.
Here are some examples of search strings on Google, good for finding info about a target company or find its employees. Of course, similar technique can be used for other purposes.
(In a Google search, the symbol * means a word or a few words.
If you put a phrase in quotation marks, Google searches for the whole phrase.)
1. Find an ex-employee of a company (change McKinsey below for your target company name; also for every example vary the number of asterisks for more results):
"I worked * McKinsey" (or "I worked * * McKinsey" etc.; vary the number of * for all of the following strings as well) "I used to * McKinsey" "left McKinsey" "I * former McKinsey"
(you get the idea)
2. Find current or past employees: "I am * McKinsey" "I * work OR working * McKinsey"