You could simply use the fresh feel to the site to your advantage. Simply write an introduction making the new members feel as though they are starting something IMPORTANT, and let them know there will be plenty of profiles to come. People love to feel like a veteran in the various sites they subscribe to- such as this forum, for example. People here LOVE to be able to say they were here "back in the day" and many enjoy helping the noobs. In any online community, these members are important to have and keep.
You could also phib initially about the number of members, although that depends on how the site is set up.
You could also do a beta period, a soft opening, or any of the methods mentioned/not mentioned above.
Either way, good luck!
