Also, they can reach out to user groups, webinars, email marketing etc.
It can be hit or miss. I have found at times that it's more management than it's worth. Most of the time I have instead taken the same budget and hired a part time virtual assistant for the same tasks and gotten better results.
Now, there's certainly something to be said for building your community and hiring local interns from local colleges in order to give back. I do think that's a real and important motive. If you are set on an intern you might reach out to marketing professors at local colleges and see if you can back channel and isolate great students from their classes, though at this point in the season you are going to be late. Most internships for top students are going to be solidified early in the Spring.
This goes without saying for any job, but you want to make sure you carefully write down and explain expectations and remember this will be someone who has not worked before (much) so things you take for granted with an experienced professional might not be second nature to them. That said, social media and online is going to be a good area for this generation of young workers.