You could also do something in which, say, the person who gives a certain page its 50th like would be rewarded. That way you don't get spammed by likes. You could make this a thing for every page, random pages, every other page, whatever floats your boat. The same thing could be done for the 50th comment, or whatever number.
Some people go out of their way to give achievement rewards to the 100th subscriber, or what-have-you. For example, someone reached out to me to say that I was their 1000th comic subscription. How you decide to reward that one person is up to you. There are lots of ways to make little random rewards like this. You could even reward people for having highly liked comments.
Just thought I'd throw some more ideas out there if you are still contemplating some 
