Hi! My clients have successfully hired VA's through Linkedin by submitting a 3 steps hiring process with a pre-qualification and assessment build in.
Also, when people continue to leave your company, I usually look into how clear is the direction of the company, is there a concise mission and vision statement, clear goals, and a goal setting framework that aligns everyone in one direction.
Also a common thing I see that make people leave is the absence of clear and articulate company values that are used during the hiring process.
Confidentiality is all about setting up the right NDA/work contract structure.
These points will help! Good luck