‘ALWAYS SUNNY’ STAR: STALKER EMAILED ME BLOODY FINGER PICTURES

Thesy Surface -- the actress who plays the creepy Margaret McPoyle on "Always Sunny in Philadelphia" -- has turned to police for help, claiming a stalker's been harassing her online ... even emailing her pics of an animated finger spelling the c-word in blood.

Police obtained a search warrant to investigate the anonymous sender -- and have traced the messages back to a Tumblr account by the name of "dirtythesy."

According to the docs, police successfully retrieved the user's email address and IP address late last month -- and plan to pursue a criminal investigation.

Police believe the mystery person first made contact with Thesy via Twitter -- posting a long comment on one of her videos, calling her "ugly and untalented."