A survey for H2CO 6 cm emission toward young massive stellar objects has been conducted using the 305 m Arecibo Telescope. We report detection of emission toward IRAS 18566+0408, only the fifth source in the Galaxy known to show H2CO 6 cm emission. A cross-scan shows that the size of the emitting region is smaller than the C-band Arecibo half-power beamwidth (i.e., θs<1'). We detect extended H2CO 6 cm absorption around and toward the emitter position. We detect H2CO 6 cm absorption features toward all 15 sources observed. Three of the sources exhibit complex absorption profiles that could be due to absorption partially filled by emission.