Drew Barrymore can't seem to get away from an alleged stalker, because the dude popped up at her Southampton estate, days after freaking her out at an NYC ... but this time cops busted him.
Law enforcement sources confirmed to TMZ ... there is an "ongoing investigation" into Chad Michael Busto showing up uninvited Wednesday at Drew's Hamptons farmhouse.
According to the New York Post, which first reported the story, Busto went house-to-house in search of Drew's $6 million property. After he found it, Busto walked onto some steps outside before police took him into custody. Drew was apparently not home at the time.
The scary incident comes 2 days after Busto struck fear into Drew as she was interviewing singer/actress Reneé Rapp at the 92NY in Manhattan. Busto, who was in the packed crowd, ran up to the stage and screamed at Drew, "You know who I am, I need to see you at some point."
Video shows security guards quickly responding and escorting Busto out of the venue, but he was not arrested. During the commotion, Drew and Renee held onto each other as they zipped offstage, only to return a short time later to finish their chat.