Nothing new under the sun. Someone did the base idea, but they haven't done it the way you did it. And if you only found out after you were already working on it, then chances are they're different enough in excecution, anyway.
Accusations of plagiarism can happen though, and on that case, if you care, you can strategically change some key things, like names, a character design with really similar colors, or an identical line. But I don't think anyone should drop it altogether, no.
Absolutely continue it! Even if it's the exact same premise and characters, you are given the oppurtunity to do it better than your similar minded peers or at the very least, more suited to your personal tastes 
Ya just need the confidence and willpower to see it through~
Just because the basic idea has already been done dosn't mean you can't do it yourself! There are many beloved stories and topics which have the same basic premise but are individually loved! Putting your own spin on a story can make a lot of difference after all.
A lot of folks say that there's no original ideas which is relatively true. There's a lot of things that share a similar base concept but the execution is what differentiates how they operate and are observed. I think a lot of people forget that part but it's all in how things are put to motion.
Some ingredients are rarer than others but you can use the most common of ingredients and create a unique flair of a popular recipe.
It depends.
If the concept is the same but the execution is different, then I wouldn't think twice about it. But if by some circumstance both the concept AND the execution is similar to how I would've done it... I'd probably put that story on a lower priority and work on something else while following the similar story written by someone else. After all, I'm writing to tell more stories of the kind I want to see in the world. If someone already told a particular story in a way I liked, why not focus on something that hasn't been done instead?
Oh yeah. My story will be written in my style, it will have characters that I made and will have my ideas, opinions, and messages baked into it. Heck, just think of any genre of comic, game, anime, cartoon etc. Think about the very specific rules and tropes that show up in them. At one point someone was the first person to do that. Then more people did it, and now it's a full genre. It's ok for more that one of a kind of thing to exist.
Once a teacher said: There's no such thing as original idea. Everything has been done before, every movie is filmed, every book is written. It's all about what are we gonna bring into the story.
Well, this kinda helped with my insecurity about struggling to find an absolutely unique idea and ending up with anything. So my answer is yes, I would continue and enjoy myself.
keep going, no idea is original anymore. Everything is just a conglomerate of influences from previous material.
Yup. Just because someone has done your base idea doesn't mean you don't bring anything unique to the table. You can always put something into your work, because nobody is you.
I mean, I did! Do you know how many other webcomics are about somebody's dead girlfriend? Probably at least like... 12, at least.
I had the opportunity to meet subjects that were similar to the ones in my comic and even the characters were just like mine but without tattoos. it was depressing but I didn't stop drawing. if drawing makes you happy, don't stop, ok?
Yeah, honestly. My concept isn't new at all. But I try to make little adjustments that help the story stand out. It has a lot to do with my inspirations. If it's eerily close, turn the story to a completely different direction, or introduce a natural element that shakes up the story. Plus, it can help with the pitch. Oh? You like Series A? Then you'll probably like Series B (your series), similar concept, but this one has [insert your interesting appeal twist here]! Check it out!"
Not to mention, my big fear is a story I wanted to tell will be told before I can even finish planning. Rising of the Shield Hero and Chainsaw Man explored concepts I wanted to go over, but with how massively popular they are, no amount of time/skill developed will compete, so I'll keep polishing it till it has an Identity of it's own. Plus, I can learn from those series in what they did right and what could've been done better.
TL;DR: Yes, if you truly want to make that story, then make it. Just make adjustments to make it stand out.
There could be many ideas that follow similar formulas, or set ups but it depends on the creator to turn those ideas into something that is entirely their own. I have seen works that are similar especially under the same genre they are but each contain their own twists or concepts that turns what would be a common idea into something that sets it apart from all the others. For my story I'm inspired by a lot animes, light novels, or mangas that are out there. One of my biggest inspirations comes from Rise of the Shield Hero. These inspirations helps me as a writer to set up my own stories to create ideas that are my own.
That's why when I'm writing my novel I picture my scenes like they are being played out like an anime. Even when it comes to public domain stories like Tom Sawyer, A Christmas Carol and others. There are so many adaptations but there are some out there that twist and create a new concept that leaps from its original source to something that becomes its own original concept of it. I think there are endless possibilities for any ideas that are created and they are different depending on who the artists and/or writer is.
If your idea is so vague that it can be done by someone else and then the idea is gone, then your story wasn't specific enough, wasn't "you" enough. That's my outlook on it.
keep going and try to give it your own unique twist to it to make it stand on its own. After all, they say everything has been done before.
Eerily close I personally couldn't continue 
Same general concepts/synopsis are fine, I think it's almost impossible to be completely original
But extremely similar execution, story beats/plot progression & unique twist is a no.
