“Guys, come check this out…”
Some people dislike that kind of generic greeting; some people (like my Mother) are offended by it actually. After all, roughly half the population of the planet are not guys. It’s also a very casual way to address someone, unless you know them quite well.
There aren’t a lot of great options for situations when you are addressing a group of people you don’t know. However, a better option would be “Dear Reader” or some variation of that as it applies to the letter or email you are sending. It isn’t as generic or overly casual and it directs your email to whoever is reading it rather than anonymous ‘guys’.