The theoretical spectral energy distributions of cool substellar objects (brown dwarfs and extrasolar giant planets) predict that these objects will shine more brightly in the thermal infrared than at shorter near-IR wavelengths at ages of >~30 Myr. Nearby stars tend to be older than this limit and a 3-5 micron high contrast search capability enables one to probe physical separations comparable to the giant planets in our own solar system. Here I will summarize recent efforts to use the new Clio 3-5 micron imager, in conjunction with the 6.5-m MMT adaptive optics deformable secondary mirror (MMTAO), to image nearby stellar samples for brown dwarf and extrasolar giant planet populations. Recently, a short observation with Clio was able to place the strongest upper limits yet on the mass of the hypothesized dust-perturbing companion to Vega (<7 Mjup; Hinz et al. 2006, astro-ph/0606129). I will present preliminary results from three surveys of nearby stellar samples, including the nearest A-type stars (Mamajek et al.), the nearest, youngest solar-type stars (Heinze et al.), and the M-type stars within 6 pc (Apai et al.).