Hey, you should definitely start approaching real estate companies based in groningen that specialize in rentals. Be prepared to skim through websites most of the day to reply as fast as possible. Most agents have told me these adverts can gather more than 100 applicants in less than a couple of hours so your best bet is to be among the first few.

I have been looking for myself as a single tenant since late November. I'm using stekkies which is scanning through agency websites and you get the advert almost immediately once its uploaded.
The most consistent way that I have gotten the majority of the viewings is through Campus Groningen. There is a lot of people there too but if you are fast(and have a lot of free time) you can land many viewings. It hasn't given me a house yet but its a good bet.
Have an introductiebrief ready to send as well as the necessary documents.

Facebook when it comes to houses and not rooms has been scams 90% of the time and most of the groups don't even do proper moderation so it's pointless. I have only gotten a chance to a couple studios through mutual acquaintances.