The key word here is "access", meaning it should be an available option for them. No woman should be forced to have a child she does not want or cannot care for. Biology does not have to be destiny, and should not be in a world in which women have supposed equality. Teenage abortion is no different except in the sense that the teenager may be engaging in activities that are unwise or unsafe, or may be being exploited, so perhaps it deserves special consideration in terms of offering counseling.
Abortion is a touchy subject, but when it comes down to it, it's a personal and private matter. To some, religious plays a part, but again, that's a personal call. A teenager, no matter the circumstance, shouldn't be forced to birth a child against her will. Should counseling be involved? Absolutely. Teenagers should understand all options open to them, but ultimately, they should not be denied an option.
I want to assume that teenager is someone who is 17 or younger. I think 18 and 19 year olds are technically teenagers but since they are classified as adults should not be included in this debate.
Minors who choose to have sex need to have options. My knee jerk reaction is yes, they should have legal access to abortion because if we do not allow legal access to abortion they will gain access illegally. Most people would agree that this is a sad situation in any case but is much worse if a girl bleeds to death in an ally way after getting a street abortion because she did not have legal access to an abortion clinic.
Abortion should never be used as a way for a teenager to abort an unplanned pregnancy that was a result of unprotected sex that the teen consciously engaged in. However, if the teen's life is in danger if she continues with the pregnancy due to health problems with the baby, or if the teen was a victim of incest or molestation and will face mental and physical anguish, abortion should be an option.