Happened to me too, I have a friend on steam who hasn't logged in for 14 years now.
Now I didn't really talk to him much back then, or really remember any of our conversations back in 2009/2010 beside the fact that I would send him a new crazy frog meme daily, but i know as a fact that I must find out who he was so that I can finally have closure in my life and finally be at peace. I've already tried most of what you've mentioned in the original post, voodoo dolls based on my singular memory of him (killed my pen pal in south africa, oops), weegee board communication at 3:33am and accidentally summoning incomprehensible horrors from another realm, goblin darts, bulgarian bloodletting to force the horrors will to give me answers as to his whereabouts.
All of them were dead ends, except for one.
Before he disappeared he had sent me one picture of his new desk and I, being a connoisseur of fine desks, immediately recognised the material; cheap, cardboard-like, recycled thin plywood from Ikea.
Using this and a hacker I had hired from CraigsList for 5 dollars and a baggie of crack, I was able to retrieve the sales data from Ikea for a period between 2009 and 2010 which, thanks to poor data security standards of the time, also contained personal information of the buyers which I could easily use in a slow and tedious process to find my old internet friend by tracking down each customers current address and visiting them myself.
As of writing, I am still in the process of scrubbing through the list and have been arrested 3 times, maced 16 times, shanked 4 times, and hit with a poison dart once.
It's a long and painful road, but it will all be worth it when I can finally ask him what he meant by "I don't want to talk to you anymore" and "Crazy frog isn't that funny, please stop".