Errr... search tool? Are you saying you have a reading list that's that long? Or do you have an entirely different definition of what a reading list is?
I generally prune my reading list quite regularly, removing finished series that I am done reading as well as looking for and removing series that I thought looked worth picking up but no longer look interesting to me.
So, assuming you have a proper reading list, all you do is go down your list looking for something off it you want to read, and if you keep skipping over stories that you've never started then you might want to consider removing those stories you keep skipping from your reading list.
If you don't want to remove it, well then maybe it's worth reading and you should start. If your response is "but I really don't think it looks interesting enough to read for... whatever reason." Then, that means it really wasn't that worth keeping around after all and you really should just get rid of it. So, stop stalling already.