Messaging someone I’ve never spoken to before

I would like to message someone who I have on Snapchat, I think she’s pretty - the problem is I have never spoken to her before in person or on Snapchat (I think I must’ve added them ages ago - I can’t remember!). I wanted to ask everyone if this was weird or not, as if it is, I wouldn’t want to make that person uncomfortable in any way and I’ll just carry on about my day and not bother messaging her.
If it isn’t weird, do you have any advice for what I could say? Do I just pop up with the “hey, how are you?”??
My mates I think seem to message people out the blue and get to know them, whether it’s in a friendly way or that they’re looking for more - I‘ve never done that though as I’ve always been unsure on how it would make people feel.
Any advice would be great as I’m pretty stuck on making a decision!
Thanks!

Tell her she looks pretty. Might seem forward but in my experience people love it when you compliment them on their looks (note: without being creepy of course). Especially online where they've posted their pictures. Doesn't even matter if you like them or not, if you think she's beautiful or has amazing eyes or there is something you like just tell her. In most cases you'll get a happy thank you.