Published to tie into a promotional contest to deduce where the Cap'n had disappeared to (Spoiler alert: he was in the Milky Way), here's the two-page Spider-Man saga I like to call The Search for Crunch:
Geez, Spidey didn't search this hard for the killer of Gwen Stacy.
Still, the promotion was so successful that Quaker Oats revisited it in 1999 by creating the teeth-rottingly yummy Mystery Crunch cereal, sending the Cap'n off into limbo for several months as everyone tried to discover where he was. Mulder and Scully actually even spent fourteen episodes searching for him on the sixth season of The X-Files. No Spider-Man tie-in for that period, I'm sorry to say, as Spidey was busy still trying to live down the Clone Saga to play breakfast detective.
Still, we are indebted to the "Where's the Cap'n" promotion for giving us perhaps the ultimate Spidey/J. Jonah Jameson face-off: