Unless they are really good videos and who ever is uploading them is pulling in massive amounts of views, I wouldn't waste the time searching for copied videos.
By not reporting them, you are losing views (it doesn't matter if it's 5 or 5 million), letting them build and grow their channel off of your hard work, and, depending on what else they upload or do, risking them put your name in a bad light.
Even worse is that you're letting them get away with theft and, by not doing anything, you're essentially saying that they can.
It takes virtually no time to do a couple of quick searches and, since you can add numerous videos to one report, the whole process can be done in under 5 minutes.
I'd much rather know that my work remains my own, that their copy has been taken down, and that the thief has received a copyright strike against them making them less likely for them to steal from me (or anyone) in the future.
Yes, I wish the process was more automated or that I could get into the ContentID program, but, unfortunately, that's reserved for the massive channels with thousands of videos.