Advice for finding someone to repair a plumbing problem?

We have recently noticed water coming up between linoleum sections in the hall bathroom, and we're thinking that the pipes under the toilet or under the bathtub are old and leaking. (it's an older house, built in the 50's). I have also cleaned a bit of mold from around the baseboard, so I think that the leak may have been present for a while. I'm not really sure how bad it is. The water leak needs to be repaired pretty soon so that we don't experience more mold growth or other structural damage. What type of professional should we call - a plumber or a general contractor? We don't need to re-do the entire bathroom - just repair the water leak. (although it would be nice to replace the floor, too!) This is our first house, and our first maintenance problem that we don't know how to fix on our own. Any advice is appreciated. Thanks!