Is there a web site where adopted children can post their history to be reunited with biological parents.

Yes but sadly there are probably over 50 of them, so the odds of each party posting on the same one. Sad they can't all agree and make one large group.

Do a web search adoption or adoption matching and several come up easy

Please do not listen to any negative people in this world. Especially being an adoptee, finding your birth family, or the what if's.
If You are an adult an angel can help you. If you are not you can still search if you want and/or can online. Your birth mother and father are adults. He/she maybe searching for you. And it is up to you and your belief system to decided what is best for you and your first family and to search for him/her. There have been many happy reunion's. Don't let anyone tell you differently.
There is an adoptee support group: Yahoo! Groups as well as many others. You can do a browser search on the yahoogroups.com website and or googlegroups.com website.
May I suggest you start of there. It is very helpful to share your experiences as well as read other's experiences who have undergone the same things that you yourself have undergone. I have. And receive support and assistance in your search process.
Also, most adoptees decide to register with Adoption.com - Information on International, Domestic, Child & Agency Adoptions, Stories, Laws -. If there birthfamily is searching for them, in all likelihood they have registered there as well. Just leave a current and update email address. Because it may take time and you don't want to miss the opportunity by not having an active email address if he/she does try to find you.
There are many support groups for adoptees as well as birth mothers, and adoptive parents. More and more adoptive parents are realizing the necessity of knowing and having good communication with their child's first parents. It is no longer taboo. And open adoptive the mainstream today.
Please check at the Yahoo! Groups site and put in adoption in the browser search. Select a group that will assist you in your state or the state of where the adult adoptee was born. You will see how many people are in the same situation as you are in. Not everyone is negative about adoption. Some are, and you have to feel sorry for them.
But I am sure you have lived quite long enough to realize there are people out there that just want to discourage you. Discourage you from wondering, discourage you from searching yourself, discourage you from your getting your information, discourage you from searching and reunion.
Everyone is different. Everyone's path in life is different. You may just find your first family waiting for the past 29 years to find you. Please do not let anyone make you feel that you do not have any rights to search for him/her and find out if they are willing to reunite and or speak with you. He/She is an adult now. And You are an adult now you can get the help you desire. And you and they can make up there own mind. There are millions of adoptees such as yourself searching and seeking a reunion. There are millions of birth mothers that are searching and seeking a reunion. There is presently an adopted chatt, somewhere. I do not have the link to give you. Do a browser check/search.
Get the support that is long overdue with a support group. Register with Adoption.com - Information on International, Domestic, Child & Agency Adoptions, Stories, Laws -, you never know if she/he is desperate to find you. Register with ISRR, International Soundex Reunion Registry, ISRR . com , Index of Search and Reunion Resources. And find out if there is a State run registry were the you were born or if you can register with them.
Again, he/she maybe waiting for you to register. And maybe not. But you never know until you find out yourself. You have a right to find out. I have.

Do youknow what your parents names are? I am looking for two of my boys who I gave up for adoption. One born 1986 and one born 1984.

As a teen, you may not receive help from an adult adoption search angel. But that does not prevent you from setting up a blog. Or interacting with other teens about adoption. And you may encounter many negative people in this world upon your journey. I wanted to warn you. But if you have determination and courage in any endeavor in life, you can succeed in learning something about your future in knowing about your biological parents. And in doing so, knowing far more about yourself than anyone or anything you could have ever imagined. Take it from someone who knows!
I have to give lynnfarnham my applause for her courage and determination.