So, I've heard getting an online following is REALLY important if you want to get an agent.
The problem is, it'll be hard to get my parents to agree to me even having a Facebook account. So, how essential is it? Will agents just drop my query if they can't find me online?
If you're writing non-fic, having a platform, which might include an online following (if you're a recognized expert, likely no one cares there either, but I'd wager you don't hold a Ph.D and a prestigious teaching position if your parents are dictating your online activities), can be important.
If you're writing fiction, it's got nothing to do with anything at all. Most agents couldn't care less about your online presence -- some might check if you have one, but they're more checking to just get a general impression (hint: if you've got pictures of yourself marching with a tiki torch in Charlottesville, that will cause agents to run.), not count your followers.