Young Jeezy Sued -- You Jacked My Song ... Claims Mystery Rapper

Young Jeezy just got called out for allegedly ripping off a Wisconsin rapper ... who must be in witness protection because it's hard to find any trace of him or his so-callled hit song.

Christopher Syrrakos -- whose rap name is Big Chris -- claims Jeezy's summer hit, "Me OK" ... is just a ripoff of his song "13 shots."

In the suit, Chris claims he dropped "13 shots" a full 5 years before Jeezy's track.

But here's the odd thing ... we can't find a trace of Big Chris' song or album ("Big Chris Uncut") on Google, iTunes, or the Internet ... in general.