Renting a server in a reliable jurisdiction that doesn't care about prostitution would be a giant first step. Germany or the Netherlands comes to mind.
The rest really depends on how much tech fiddling you can expect from the audience. Obviously, just using a normal SSLed website has the lowest barrier. You would have the option of using Tor on the client side, but you could still access the thing with a normal smart phone if need be.
The next step up would be a site that is reachable only via Tor. This would (within reasonable limits) give users privacy of connection. However, if they exchange real phone numbers and other contact data - which they probably need to - this advantage becomes moot.
Encrypting private messages between two or more parties so the host can't read them would require users to keep and manage their own key rings. That's not a reasonable expectation. In any case, the most important content would probably have to be available to all users, such as client information for screening or a general community support message board.
The rest really depends on how much tech fiddling you can expect from the audience. Obviously, just using a normal SSLed website has the lowest barrier. You would have the option of using Tor on the client side, but you could still access the thing with a normal smart phone if need be.
The next step up would be a site that is reachable only via Tor. This would (within reasonable limits) give users privacy of connection. However, if they exchange real phone numbers and other contact data - which they probably need to - this advantage becomes moot.
Encrypting private messages between two or more parties so the host can't read them would require users to keep and manage their own key rings. That's not a reasonable expectation. In any case, the most important content would probably have to be available to all users, such as client information for screening or a general community support message board.