I'm looking for some songs I can play on an acoustic guitar.
I want them to be fun, a little uptempo and most importantly: well-known so people can easily sing along.

well, there is Bad Moon Rising by CCR... or Sweet home alabama... or All sommer Long.... or anything like that really...
To The World I Am A Stranger, To A Stranger I Am A Possible Serial Killer

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You guys are so funny xD xoxo <3

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Well a human can't sing an Em since that's a chord

If you mean Eb3/E3, then that is a contralto voice.
Well if you're playing in pubs I think these songs might work.

Mumford and Sons - The Cave, Little Lion Man, Babel, I Will Wait
Lumineers - Ho Hey
Of Monsters and Men - Little Talks
Neon Trees - Animals, Everybody Talks
Counting Crows - Mr. Jones
Tom Petty - American Girl
Bruce Springsteen - Born to Run
Elvis Presley - That's Alright Mama
Gin Blossoms - Hey Jealousy
Edward Sharpe - 40 Day Dream

And on

and on
"Pain or damage don't end the world nor despair, nor fuckin' beatings. The world ends when you're dead, until then you have more punishment in store. Stand it like a man, and give some back."
Yes "Wonderwall" too. Or "Song 2" - Blur. Even in acoustic everybody can sing "Who-hoo". "Island in the sun" is easy and well known too. Is it still uptempo enough?
Or maybe some old Beatles songs? Like "Day Tripper?" It depens of the audience...