Scarleteen

I've heard tell that there are such things as discreet forums where people post arousing pictures of themselves, or have group masturbation sessions. Are these real? Are they safe for teenagers? And if so, where could I find one?

There are spaces online where people share photos of themselves, and have sexual conversations either over text or voice/video chat, but they are adults-only spaces; any place like this online is going to be only for people 18 or older.

Yeah, now that I think about it, that almost definitely be considered child pornography... I would say lol, but that would make it sound like the subject is a joke

Yes, there are issues both of child pornography (which people can get in trouble for even if what they're sharing are images of themselves they've taken/shared willingly) and that any sort of adult-focused website will want to work very hard to make sure they aren't letting anyone underage join or contribute content because they won't want to be shut down or open to any legal action. I get how you wouldn't necessarily think about that immediately but it's definitely going to be the case, and honestly if you did find a site that was open to underage users but that encouraged that sort of sexual content it would likely be a very unhealthy/unsafe environment.