Imagine this is the relative effectiveness of inviting people:

• 50% Endorsement. (If someone endorses the meeting, half of the people invited will come.)
• 10% Referral. (Looks like an endorsement is five times more effective than a simple referral.)
• 3% Two-step. (Get someone to answer an ad, and then send them more stuff and invite them.)
• 1% Cold call. (Gee, you would have to make 50 cold calls to equal one endorsement.)
• 0.5% A simple email inviting a person to your meeting.

These are relative numbers, but you get the idea.

Instead of running ads, etc. – make personal contact with one, two, or three people. Build a relationship and invite them. That will be more effective than hundreds of emails.