  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 photo detectors 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.
