I'm looking for advice on how/where I should advertise to get the most engagement, especially with fellow STR investors.

Also give you time to advertise 

It was from word of mouth advertising from those initial 34 guys.

Where are you advertising at?

I was hoping to find someone with experience/ alternative websites for advertising an international medium term in the USA

you may want to strongly consider being the bank on a good portion of this cash. owning rentals that you do yourself is a lot of work .. and BRRR even more so with a ton of risk if you have no experience at it.its only my thought process but if your going to buy rentals I would by top shelf not the ones that advertise the greatest returns you U take on risk with those. 

(tenant to pay)- I had a property manager come out to the house who estimates the monthly rent at $1,500 - $1,700 (without advertising it, they'll share it with the "network of tenants" they've developed over time).

If you list the entire house and advertise it as a student rental, groups of friends will naturally want to rent it out, and they'll just split the cost between them.

We advertised it and for about a week or so got no response.

Finding homes to flip in this condition can be done through popular online listing websites or through manual and creative methods like searching public records and advertising on signs.