For a social media startup, what can be the strategy to bring students to test the App?

What I'm going to offer something that is a bit tricky and you need to use it with a lot of caution. It will also require some development.
One of the ways of growing fast and get additional users is by having current/ new subscribers to send their contact list a notification that they have joined your app and offer these contacts to join as well. You can add a screen after the first installation suggesting to send an invitation to certain friends (based on location. e-mail address/ Facebook criteria etc.), but you must make sure it is an opt-in option so you won't get your app spamming the current users contact list. This way you generate more users from current users sending them an invitation to try your app.
Does that make sense? I will be happy to elaborate if needed, just send me a message.
Good luck

Perhaps you might want to offer to come to a class and speak about entrepreneurship, programming and startups. Find a way to give first, and then at the end let them play with/use your app.

You can't go wrong if you are offering more than you are asking for.

Also, research has shown that you can get 80% of the information that you need from User testing with just 5 users. You might be able to get a lot more done with less people than you suspect.

The Test strategy should make sure that all the quality and performance guidelines are met. A few pointers in this area:
1) Selection of the devices – Analyse the market and choose the devices that are widely used. (This decision mostly relies on the clients. The client or the app builders consider the popularity factor of certain devices as well as the marketing needs for the application to decide what handsets to use for testing.)
2) Emulators – The use of these is extremely useful in the initial stages of development, as they allow quick and efficient checking of the app. The emulator is a system that runs software from one environment to another environment without changing the software itself. It duplicates the features and works on the real system.
Types of Mobile Emulators
Device Emulator- provided by device manufacturers
Browser Emulator- simulates mobile browser environments.
Operating systems Emulator- Apple provides emulators for iPhones, Microsoft for Windows phones, and Google Android phones
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath

Give your app to 5 or 10 students and provide an easy way for them share it with friends. If they don't share it ask them why and you will learn a great deal about what needs to be changed so that they start sharing it. If they do share it, ask them why and you will learn about what to do more of.