I haven't seen or heard from my dad since I was 6, and I haven't lived with my mom since I was 15. So I know from experience that it really does effect you a lot. It shows you how hard the "real world" really is. You have to mature, and grow up a lot faster than most teens.
What you'll see in parentless teens is
Rebellious
Low self-esteem
angry
crude
avoidant
anti-social
depressed
prone to violence
envious of teens with parents or try to become closer with teens that have good relationships with their parents (depends on the teen)
unable to support their own children (when and if they have any)
and become awkward when placed in social environments.
Humm - is this information for a school assignment? Just wondering ...