"Hey, how are you?" is all you need in my opinion. There's no need to overthink it. If they're interested then they will reply to you. And don't worry about messaging people that you match with. Simply message people you find interesting. Try to avoid complimenting their appearance also. Might sound odd, but it's pretty obvious to them if you're contacting them. Save your compliment for the first meet when they look their best! But if you must, avoid words like "sexy" or "hot". At least for me, I get the wrong impression.
- Bingo. You can just ask them where they are from, or any other normal conversation starting question. There is an old saying...... "You had me at 'Hello'".