We present results of an optical and near-infrared (IR) 1.8 deg2 survey in the Pleiades open cluster to search for substellar objects. From optical I-band images from the CFHT and J-band images from the 3.5 m CAHA Telescope, we identify 18 faint and very red L brown dwarf candidates, with I> 20.9 and I-J> 3.2. The follow-up observations of nine objects in the H- and K_{ s}-bands confirm that eight belong to the IR sequence of the cluster and the proper motion measurements of seven candidates confirm that they are Pleiades members. A preliminary estimation of the substellar mass spectrum dN/dM in the form of a power law M-alpha provides alpha=+0.57±0.14. We extrapolate this function to estimate the number of very low-mass brown dwarfs and planetary mass objects that could be present in the cluster down to 1 M_{ Jup}. Sensitive searches combining far red and near infrared observations may unveal these objects in a near future.