Make sure your child is the appropriate age to use the social network site.  Facebook and MySpace are generally geared towards adults and have a minimum age of 13 years old.  Some sites are geared towards children such as Whyville (Ages 8 - 15) and Club Penguin (Ages 7 -13). 

Regardless of the site, you should check it out ahead of time to see what features it offers, what information it requires your child to share and what they do with that information (privacy policy).  

Make sure that your child isn't posting too much personal information such as full name, date of birth, street address, cell phone number or your name.  Other information such as hobbies, sports played and schools attended can provide vital clues to your child's location.   I use the analogy of a puzzle - the more pieces (of information) someone has the easier it is to see the big picture (child's location).

Your child should only post information that you – and they – are comfortable with others seeing. Remind your child that once they post information online it is there forever. Even if your child deletes their profile, older versions still exist on others’ computers.  This is especially true for photos.  Pictures really are worth a thousand words and can be used to gain information about your child's school, location, etc. Inappropriate photos can lead to damaged reputations, school sanctions and criminal charges.  People have been kicked off sports teams, lost college scholarships and not been hired by an employer on the basis of photos posted by them or someone else.

Enable privacy settings on your child's social network site so that what they post isn't publicly available.  Urge your children to not add anyone as a "friend" unless they know them in real life.  Periodically check your child's site to make sure they're doing this.  The best protected and most private site is easily defeated once your child adds someone they don't know.

Talk with your child about using online "netiquette".  Your child should understand that people should be treated with respect in real life and online. 

Routinely check the social network site(s) your child uses to find out whether or not they are making responsible choices about the information they share, who they talk to and how they treat others online.  If you find that your child is not acting responsibly, use that moment to correct this behavior just as you would if the same thing happened in the real world.

Encourage your child to report anything that is inappropriate or makes them feel uncomfortable or scared.  This could range from an inappropriate photo to a threatening message.  Let them know they won't be punished for reporting it to you.  Many children don't tell their parents because they are afraid they will lose computer, internet or phone privileges.

Spend time online with your child learning what sites they use and how they use them.  Be involved in your child's online experience just like you would if they participated in sports, band or church.  Even if you don't know much about a computer, the internet or Facebook you will be amazed what you can learn from your child when you share those technology experiences with them. 

OnGuard Online  http://www.onguardonline.gov/
Focus on the Family  http://www.focusonthefamily.com/parenting/
protecting_your_family/articles/family_safety_resources.aspx
Wired Safety  http://www.wiredsafety.org/resources/pdf/socialnetworktips.pdf
Stay Safe Online  http://www.staysafeonline.org/
Safety Web  http://www.safetyweb.com/online-friends
Federal Trade Commission  http://www.ftc.gov/bcp/edu/pubs/consumer/tech/tec13.shtm
Safe Families  http://www.safefamilies.org/socialnetworking.php
Common Sense Media  http://www.commonsensemedia.org/social-networking-tips
Safe Kids  http://www.safekids.com/
Safe Teens  http://www.safeteens.com/
Simple K12  http://www.simplek12.com/internetsafety
Facebook for Parents   http://facebookforparents.org/