Decentralized Online Social Networks (DOSN) seek to increase their users' privacy by removing centralized data storage and control. Their lack of usability and competitive features has severely hindered their success. Even a privacy preserving user discovery, which seems paramount for a social networking service, so far has not been implemented. Aiming at a hybrid architecture of decentralized servers, as it is suggested by the currently most successful DOSN Diaspora amongst others, we suggest a distributed discovery of users. Our discovery mechanism protects privacy of users and does not create vulnerabilities to mass collections of profiles or SPAM. The scheme adapts known techniques like DHT, indirection, and proof of knowledge, to meet the service specific requirements. A general implementation for a popular XMPP server furthermore gives proof of our concept and represents a first step towards constructing a reliable distributed social networking service with user discovery on decentralized servers, without leaking any information about its users.