How can I get big web execs listen to my idea for a website-?

I’m not a businessman of any sort but I am one of probably thousands out there who think they have the concept for the next big thing in the hugely profitable internet retail / shopping business. The people whom I’ve told the idea all said it is indeed going to be a hit ( even globally ) and some advised me to have a non-disclosure agreement if I actually end up pitching to a web executive. These past weeks I have sent emails to both executives and low level management staff of the biggest web entities out there but no one paid attention. One company actually did but even that one gave me a very kind and polite brush off. The thing is, this website has to be launched in a big way and not start from small to give it enough headstart that inevitable copycats won’t be able to catch up. Much like Groupon or Living Social, the two biggest discount sites out there who now have lots of copycats. Thanks in advance for your answers-!