Teenage pregnancy is entirely dependent on the situation. If the person has decided thats definitely the route she wants to take in life and she is mentally mature enough to handle pregnancy and motherhood, as well as having the correct resources for a child, then why not, although having all three of those things seems unlikely. On a personal level, I wouldnt want to be a father until at least 30, because that will give me the time to do all the other things in life other than create; even then it wouldn't be a priority for me.
As for Teenage Sex in general, I dont have much of a problem with that, but once again i would stress that both parties should be emotionally prepared for it.
Sex and pregnancy without marriage? I dont see any moral, emotional or physical reason why marriage is necessary for sex. Although, once again I think that the couple should be financially ready and responsible. What difference is there between having sex and having sex with a certificate in a cupboard somewhere?