Who makes logos? Printing, publishing companies; design agencies and sometimes ad agencies ---
1. Broadcast email to the contacts of middle tier agencies (middle tier because the upper tier will not leave its paid software and accept help from a free one).
2. Post ads on facebook applications.
3. Broadcast emails to fine arts and computer aided arts students (list can be arranged from institutes and broadcast agencies)
4. Have a contest of 'best logo' in agencies, sponsored by your website. The participants only have to use the website to create the logo.
Other ideas are on the way.... interested?