They are all scams to get your money. There are several variations
1 - they are hookers/escorts looking for new ciients who will charge you for a date
2 - they claim to be a real girl who wants to meet you but wants you to verify your age/identity/criminal background by going to some site she links you to. She will say that they will not charge money, but the site asks for all the informaition anyone needs to steal your identity AND a credit/debit card number and it will bill you $59/month for the next 36 months with no way to cancel. And you'll never hear from that girl again
3 - they want you to come to their webcam site and pay to see them on cam
4 - they claim to be a real girl and their webcam is not working for Skype, only on some other site which again will ask for your credit card details
5 - they will exchange a few messages, then claim to have an emergency and are out of town and need to "borrow" money from you which they claim they will pay back next week when they are home
6 - they want you to text a certain 5-digit number saying it gives you free texts and calls but instead is just signing you up for a premium rate text service that will bill you $0.99 for every text you send and receive with no way to cancel
Any time you cannot meet the girl in person for an actual date then they are not real. I would imagine 95% of profiles are fake