- We consider the method of entanglement witness operator to verify genuine multipartite entanglement for single-particle W states involving N parties. In particular, linear optical schemes using photodetectors and beam splitters are proposed to implement two different types of witness operator in experiment. The first scheme that requires only a single measurement setting is shown to detect genuine multipartite entanglement for the overall efficiency beyond 1-1/N. On the other hand, the second scheme with N+1 measurement settings achieves success at a significantly lowered efficiency than 1-1/N. 2008 The American Physical Society.