Alright, as we all know now, Pein (Nagato), Konan, and Yahiko knew Jiraiya when they were kids. We know that Konan and Pein are together now in Akatsuki and Jiraiya figured out that the deaths of all 3 of the kids was a lie. So, did anyone wonder what happened to Yahiko?
I think I've figured it out!!

-Yahiko-
[link]

-Juugo-
[link]

THAT'S RIGHT!
He's not with Akatsuki like the others because Orochimaru was with Tsunade and Jiraiya when they found the kids and saw his potential so he took him for his own! Now he is out with Team Hebi, but since the Leaf, Akatsuki, and Team Hebi are all clashing right now there might be a reunion up ahead!

Reasoning other than appearance: Juugo is the source of the curse mark which definately makes him powerful enough to both be in Akatsuki and wanted by Orochimaru. If they are the same person, I don't know why his name is different or if he remembers or not, but as we all know, Orochimaru loves to mess with people so maybe he messed with his memory because Orochimaru knew that the others were with Akatsuki and didn't want Juugo going in that direction because Orochimaru hates Akatsuki. Also, when they show Yahiko as a kid he is a little too into killing people for revenge because of all the people they have lost and when they first show Juugo he is sitting in his cell contemplating on whether the next person he kills should be a boy or a girl. Also, Juugo doesn't have much self control and that might have evolved from more years of war after they first show Yahiko as a kid.

Just a theory.