It's a cool idea but it's also a very easy problem to solve for free. Oftentimes it never gets to the point hr is actively looking for someone: they just use internal referrals (cost 10% of a recruiter, roughly) and worst case scenario use a recruiter.

Personal introductions also seem to net a better salary in my opinion

Companies that use only recruiters are too big / growing insanely fast or so bad employees wouldn't recommend to their friends.

Me and friends / coworkers use a free trello board / free slack community and we keep hiring among us whenever we jump ship