Advice don't count. If you talk, they talk back: they're already submitted by a stress when losing/camped, you're just providing them a way to vent out.
Everyone makes a lot of mistakes all the time. If you're not busy enough with your own, you're missing something.
Communication is great but if it's of "Be Happy! to the depressed guy" level, it won't work. A feeding player can need help. If you can't provide it or if you don't think it's worth to go out of your tracks to get him back on his, let him be, and focus on something else. He won't miraculously recover from it with kind words, that's how he's been playing for hours, he won't change on the spot.
I'm not talking back in chat because I prefer soothing than flaming, but as a bad laner and good late game player, I can tell you that: when you're stuck in a hard situation, you have to gather all your strength to think properly. Having someone making noise in the background doesn't help AT ALL. Most games I won after recovering from an awful laning phase, that's because my mates didn't tell anything and gave me room to refocus.
Give it time, that's the best help you can give from afar.