Cellular phones extend the traditional view on sensor and ad-hoc networks by allowing global communication through cellular infrastructure in addition to local ad-hoc communication. We exploit this mediation characteristic of cellular phones in a participatory sensor network supporting the search for mobile objects that can be sensed in the vicinity of cellphones but have no communication facilities. Our proposal improves upon existing geographic routing algorithms by using scoped flooding in order to take into account real-world constraints such as infrequent sensing with limited sensing ranges. We further make selective use of cellular communication to avoid the delay it takes to traverse long multi-hop routes. As we show, a well designed system reduces search delay and at the same time lowers cost in terms of energy spent for cellular and ad-hoc communication.