Do you use LinkedIn? Of course you do. We all do. Which is why LinkedIn is increasing its prices for recruiter seats (they have what you need, so they increase the price to maximize earnings).
So if you’re just spamming the heck out of everyone with copy-and-paste messages, you’re only going to get a few (lame) responses. We’re to the point where that seat is so expensive that it would be more affordable to just buy some plane tickets to your prospects’ place and hand-deliver a cake that says “Work for us!”
So if you’re going to spend the cash for that seat, use it right: Craft unique messages to each person. Stop pitching them from the first salutation. Send them materials they would want to read, not just what you want them to do. Give them the tools to make a better decision, rather than spam and hassle them until they flee.