If you're looking a purely paid opportunities, I'd focus on:
1) Facebook - develop some audiences and lookalikes around users who are college aged, currently attend college. You can target in many ways via FB, but that would be a good first place. You can then get more precise around interest targeting.
2) Twitter - same type of targeting - lower app install rates from my experience and higher CPAs. Worthy to test - but start smaller
3) Google - either through display network or Universal App Install campaigns, which show your ad across the Google Search, Display, and YouTube network. You can also designate a CPA you're looking to reach.
Start here first. In my experience, FB has been the best performer from a CPA perspective and LTV.
It's important to test creative A LOT. You can't just rest on creative creation. You need to make sure your creative matches your targeting audience.