Snapchat Co-Founder Evan Spiegel -- I'm Being Stalked ... On Snapchat!

Snapchat has made Evan Spiegel the world's youngest billionaire -- but it's also part of the reason he's calling in LAPD to nab a seriously creepy alleged cyberstalker.

In a not-at-all-funny case of live by the sword, die by the sword ... police say Spiegel received harassing messages through Snapchat, Twitter and email from a man identifying himself as Ramon Martinez.

According to docs, one email Spiegel received referenced JFK, slain actress Rebecca Schaeffer, Molotov cocktails, and cutting car brake lines.

Things got even scarier when the 25-year-old Snapchat co-founder says he got a package at home -- a letter wrapped in a gun magazine. Cops say the letter was filled with "nonsensical" messages.

Investigators are on the case.