United States copyright law would consider it a copyright violation whether or not you could contact the author or even knew who authored it.
Consider the case in which the author of that work is trying to sell it at their obscure website that you cannot find. Somebody took it off their website and uploaded it to supermegatrolled (a clear violation of copyright). You take the work and use it not knowing who the author is, or how to contact them. The author finds out about your usage and sues you.
In this particular case, it is very easy to find out who the author is. I dragged that image to Google image search to use the "search by similar images" feature. The original source appears to be here: http://neversatisfiedcomic.com/