Anyone can be anything on the Internet; someone claiming to be a 15 year old girl may in fact be a 45 year old man.
Don't ever give out personal information on your Profile or to Strangers. Profiles are publicly visible to anyone, so don't include your last name, phone numbers, addresses, school names, or anything else that can lead someone to you.
Only use sites/services like Nexopia that allow you to block Messages from people you're not comfortable with - if you're uncomfortable with the way a conversation is going, just get out, do not worry about offending the other person
If you're going to send personal information, send it as a message, not a comment, as comments are visible to the public.
Take precautions when meeting people - If you're going to meet someone, always take a friend, go to an open and public place and make sure someone you trust knows where you're going and when you'll be back. Taking a cell phone helps provide extra security.