Muudea Sedik -- a popular YouTuber who goes by Twomad online -- has died ... TMZ has learned.

Law enforcement sources tell us the internet personality -- who has millions of followers across his various YT channels and social pages -- was found unresponsive Tuesday night at his Los Angeles-area home ... this after somebody called in to ask for a welfare check.

We're told Twomad hadn't been heard from in several days by concerned parties -- and he even missed some appointments. As a result, the LADP was sent to check on him ... and that's when they found his body, although it's unclear how long he'd been in that state.

Our sources say there was drug paraphernalia found on the scene, and at this point ... we're told this is being investigated as a possible overdose. No foul play is suspected in the death.

Twomad had caused concern among his fanbase in recent weeks -- including some strange, one-off tweets he was posting last week ... not to mention a bunch of photos of firearms.

The guy was an interesting character ... in addition to skits, gaming commentary, and live streams, he was just very into internet culture -- and had a massive fan base. Like we said, millions of followers ... but his videos would also get a significant number of views.

One meme, in particular, that he's credited with is the one called "Goodnight Girl, I'll See You Tomorrow." It features a shirtless Twomad walking up to the camera and telling some imaginary chick that he'll see her tomorrow ... only to slip and fall in cartoonish fashion.

He also made a splash by once collaborating with OnlyFans model Belle Delphine.

Twomad was embroiled in controversy of late -- and he seems to have been off the radar in recent months when it came to his content creation. His last video across all 3 of his channels was 5 months ago ... and he certainly seemed to be in good spirits in it.

He was only 23.