I am thinking an attractive girl probably has a ton of guys hitting on her, so you would probably do best to demonstrate that you have read her profile and are actually interesting and can challenge her in some way (bonus if you can make her laugh). For example, try asking her if she were a superhero, what would be her special talent.
Do not comment on her looks initially; you obviously wouldn't contact her if you didn't find her attractive. I also don't know why she would want to chat with someone she's never met before, so send her a note instead.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?