This puzzle is part of a series - part 1 is here, part 2 is here and part 3 is here. Any comments I make on the OP are canonical and out of character (OOC). Any comments I post on answers are for flavour only.
You may notice there's been a bit of a delay on part 4 turning up. I think I just needed some time :-) I've kind of lost my feel for difficulty (although seeing how part 2 went, maybe I never had it :P) so if this is way too difficult I'll bust out some clues later on.
You suddenly wake up from a dream about a really, REALLY warm glove that you'd just invented, only to discover that the neighbour's cat is asleep on your hand. Groggily, you pull your hand out from under it. the cat jumps up, startled, gives a loud "Meow!" and takes off, knocking your mug of now-cold coffee all over your keyboard.
Biting back a swear word (this is a child-friendly site, don'tcherknow) you try to shake off the groggy feeling in your head. Your vision blurs a bit and you feel dizzy, so you stop quickly. Wait, why do you feel dizzy? What's that dull pain at the back of your neck? Maybe you're just missing your daily fix of riddles on P.SE - that must be it. You've been awake for almost a whole minute... probably... and you still haven't found any magical spaghetti recipes.
Hang on! There was something wrong with SE wasn't there? After a brief moment of nausea, you remember - some nut-job was attacking the Stack and you were going to track him down and give him what-for. How could you have forgotten? You waggle your mouse a bit to wake the computer up, but nothing happens. You look under the table and- holy moly, your computer's disappeared!
Looking around your room, you realise the place is an absolute tip. Well, more so than normal; if it was just old plates sitting on your desk and clothes piled on the floor then that would be normal. The door is wide open, your drawers are all opened and it looks like someone's gone through all your stuff looking for something. Looking back at your keyboard, you notice that there are some keys which are missing - apparently someone didn't want you typing anything about Marin Cilic, because the C, I and L keys are gone.
This must be related to the SErial Killer - he knows you're on to him and he's trying to stop you!
Now that pain in your head makes sense - someone must have broken into your room (you may have heard them if you weren't so busy listening to Rick Astley, maybe) and knocked you unconscious before stealing your computer and maybe even your lucky pair of Y-fronts! You wonder how long you've been blacked out for, but there's no time to waste - a world where the SErial Killer is at large (and possibly in possession of your pants) doesn't bear thinking about.
You have to act!
Frantically, you hammer on your next-door neighbour's front door. When they open it, you gabble hysterically at them, then barge past (knocking them to the floor) and rush to their computer. You pull up SE and head to Area 51, but it looks completely and utterly normal. On second thoughts, not really; all the proposals have just over 2,000 followers and the site header says "Area 151". As you scroll through the list of site proposals, it dawns on you that your neighbour doesn't normally wear a long brown coat and a fedora...
With very little time before the mysterious impostor picks themselves up and get very angry at you, you must find a clue, some way to pick up the trail and come closer to unmasking the SErial Killer.
Who should you try to contact?