Tiled wall fixings

This is really for a shower, but someone may have an answer in this section? I am looking to fix a few shelves in a shower and as it is a new build the tiles are on plasterboard. Is there a specific fitting that is best to use? Probably no more than a kilo per fixing required. The ones I am replacing have standard screws in and have rusted. Also where the previous owner used the compression type wall fixings that you use a tool on, the tiles are cracked and I will replace.
Thanks in advance.