Since I'm working with limited funds and lack of personal mobility, online is where much of my non-local marketing will happen.
Unless something changes for the better for me financially, my offline promotion will stay local or at most within the boundaries of Michigan, my home state, so for better or worse most of my outreach promo will be online, and like CK said, it's hard to reach our target readers if we write MG because they're not online in the same ways teens and adults are.
At least with picture books and early readers, we have a more direct in with reaching parents and teachers, but those independent under 13 readers are hard to reach if you don't have some hook behind you.
Something I feel lots of writers (ESPECIALLY YA+ authors who's books are aiming at teens and up) don't respect or understand, even here we have that debate often.
Now that I do video, I'm trying to share more on YouTube, because kids of any age (Teens too, of course) will go there if it's not "banned" at home and certainly many schools blacklist YouTube for various reasons. So using school-approved alternative venues like "Teacher Tube" can be a work-around-http://www.teachertube.com/
There's also "School Tube"-http://www.schooltube.com
I think the best thing any author can do is stick to what they're best at or are willing to learn. I may not attract millions with my blog, but I'm good at it, and I have full creative control and it can fit around my schedule.
I was willing to learn video because in the long run it will broaden my audience, even though we want to attract potential readers/buyers of our work, we can reach anyone with video, even kids who don't read yet.