You should always ask permission to use someone else’s work. So how much of an effort should you make to track them down and get it? You need to make a “good faith effort” which is generally defined as “what a reasonable person would determine is a diligent and honest effort” to produce a desired result. In other words, you need to do more than quick Google search before calling it quits. It’s tempting to think that because access to the internet is so ubiquitous, everyone must be online and instantly reachable. Unfortunately that’s just not the case.