Police Track Rihanna Alleged Stalker

Rihanna’s alleged stalker is about to have cops crawling up his cyber ass, searching his online accounts after RiRi got a terrifying gun threat on social media.

Law enforcement sources tell TMZ 

LAPD will scour the records of someone who goes by Alex Mercer and Ralph Alexander on Twitter and Yahoo. We're told the guy posted a selfie of himself on April 30 outside Rihanna's former home.

The next day, he tweeted,  “Should of killed @rihanna a minute back I would be good right now. Sorcery is a weapon I use guns, bout to get a gun license, can’t use my hands.” 

Police went to Rihanna's house, but he was gone by the time they arrived. So, now they're tracking him down electronically, through phone, computer, and social media records.

See photo of the stalker at Rihanna`s resident...