Is it advisable to report players who are afk in champ select and fail to respond to anything?

yes

of course! Why queue if you are afk? I mean, if they come back though before they select their champion, then I don't know...what do you guys think? Personally, I wouldn't report.

But How can you effectively report them? I dont want to go in ranked game with an afker who will either stay afk or come back and troll. And what if the afk random pick was like a second support... Can you take a screen shot and send in the logs or something to riot while dodging?