I'm having the same trouble as other people! I was running AdBlockPlus with zero problems until I upgraded to Safari v.12. Then it made AdBlockPlus (and another adblocker (Ghostery) disappear/stop working. Call in to Apple Support was pretty useless.... I did manage to MAYBE get it reinstalled. But can't tell if it's actually working now.
When I click on the Icon it says the app is enabled. But I'm not seeing the little numbers of how many ads were being blocked, which used to be reassuring, I can tell you, since spam ads routinely froze up the screen on a web forum I'm routinely on -- not to mention how many of the ads were irrelevant, insulting, and in at least one instance ILLEGAL (I had a chat with the forum's admin guy, who was not seeing the same ads in the Netherlands as I was in the US, over that one, and he just groaned and said "They're not supposed to be running ads like that...").
But now? I can't tell if the app is running or not. And on another website (which used to also have some pretty egregious ads -- and I got lots of handwringing about how they were a small mom and pop operation surviving on ad revenue)? Ads are back: some "dating" [possibly using the term loosely!] site (showing a blonde bimbo in a low-cut top who had apparently had cosmetic surgery she needed to show off)! I've sent off a screen shot of the ad to the Help desk (as well as to the site where I saw the ad, with the subject line in the latter case saying "THEY'RE BAAAACK!") but of course it's the weekend and I don't know how soon I'll hear back from ABP support. So I clicked on "help" in the settings then found my way to here after reading that I'm supposed to have an Option Menu.... But WHERE? Do I not have ABP installed correctly? Or at all for that matter? I'm not a techie! I just want to have an ad-free online experience and I USED to have that with ABP. (And to the guy in the Netherlands: No, Wim, I DON'T want to whitelist the site. Because I CAN'T. Tired of the site crashing. Tired of ads for slutty dresses from some some crooked shopping site in China, crotch shots of mens underwear my husband won't buy in a heartbeat, silicone wedding rings, BS about what some so-called reality star said about some other so-called reality star, or how to break PA law by getting a concealed carry permit online....) I've looked at the page about what is considered an "acceptable" ad -- but NOWHERE does there seem to be any consideration as to whether the CONTENT is "acceptable" -- just whether it blocks web pages or automatically runs Flash....
Oh and a couple of weeks ago, before doing the browser upgrade (which I didn't want to do before doing a back up), I was seeing popups telling me that there was a new updated version of ABP for Safari -- but I don't know if it was from Apple or ABP, and I don't know if it was supposed to be working with Safari v.12 -- which clearly, what I've downloaded is NOT.