Mobile device-to-mobile device discovery may be performed via a relay device (e.g., wireless transmit and receive unit (WTRU)), which may send a discovery request (e.g., including service ID, relay capability indication, and relay WTRU ID) to a ProSe server. A discovery response may include a (e.g., ProSe) relay service broadcast code and discovery filter (e.g., corresponding to service ID for a service broadcast by a service provider WTRU). The relay WTRU may use the discovery filter to listen for a ProSe code broadcast by a service provider WTRU. The relay WTRU may determine a received ProSe code matches the discovery filter. The relay WTRU may broadcast the relay service broadcast code based on the match. The service broadcast code broadcast may be intended for receipt by a service utilizing WTRU, which may utilize the relay WTRU to join/receive a service from a service provider WTRU.