Maybe I'm missing something, but why would you look for a study buddy on your site and not in the MOOC discussion forum (because there you will easily find people taking the same course obviously)?
Very good question. I would recommend doing both I suppose. On Stacks, we match you up with buddies based on all of the courses you are interested in rather than just one. So our algorithm may recommend that you match up with someone who is interested in Computer Science, Literature, and Psychology; rather than just matching you up with someone in your Computer Science class.