Probably the best way to find seep areas is to use some sort of acoustic remote sensing technique. Mainly because acoustic waves can penetrate the ocean. Also, we expect that the seafloor will be modified by the presence of seeps.
Hydrocarbons seeping from the seafloor change their environment in several important ways.
Many seeps build mud volcanoes where fluids carrying muds are expelled. Often these have sediment flows emanating from them. In addition, where hydrocarbons come to the seafloor, microbes attack them and a byproduct is nodules and rocks containing calcium carbonate.