Just as having your friends laugh at your jokes doesn`t make you any funnier hiring fake people to post on your site does not make your internet business any money. Just as having fake friends at a party is not going to be fun for your real friends, fake friends on a community site is not going to make your website any better.
Instead, when you launch a online community website throw up a big BETA next to your logo to inform users your site is new. Encourage them to sign up, explorer the website, and to leave feedback for the webmaster; as the site is new and needs feedback from the community.
If you have built a good internet business around an niche industry with few competitors (best ROI) users will appreciate what you are trying to build and participate. If you find yourself in a position where users are not converting to members you have to rethink your business strategy.
A good community is built around the community. 9/10 features need to be changed after the launch of an online community. You will find even if you only get 10 interested people to sign up that it is better than 1,000 non-interested people. Even if the site is empty these interested people will feel "fulfilled" "encouraged" "needed" and help you build the site, get members, and keep it active.
How do you think this site has so many forum moderators?
I agree with guerillaRed. No one likes to be first on the dance floor. You have to jump out there and do it and people will follow. You can also hire posters (I`ve seen rates of anywhere from 25-50 cents per post) to do the job for you. Do a Google search. They`re out there.