While I think it will tough to find high school student specific internships, a few ideas:

1. Talk to your guidance counselor at school. Many schools have contacts within the community to help students find internships or entry-level career-based jobs.

2. Check non-profit organizations. While the opportunity may be volunteer-based, meaning you won't be paid, many offer real-world opportunities. For example, in the DC area you can search the Washington Post job site for volunteer jobs. There are hundreds, if not thousands, of positions for everything from office admins to web developers. I would bet the Chicago Tribune has similar listings.

3. Building on #3 you can also search for internships in the job postings, although not sure how many will show up.

4. Attend meetups in your area and network with other attendees. Talk to them about opportunities.

Good luck!

I suspect no one will post any jobs targeting high school students. If you want to get something, I suggest finding a list of startups in the area and email them individually, listing the things you've built.

Summer intern for highschoolers == spend your commitment free life doing tutorials online and learning how to code!!