If the individual has a green card (Permanent Resident Card), it would not automatically make you a citizen. The individual themselves is not yet a full citizen. In order for them to petition for you, they must first apply for citizenship themselves. The green card (Permanent Resident Card) gives the individuals the rights of a citizens but they are not 100% a citizen. They must commit to the next step, which is the apply for full citizenship. This involves an examination and the oath of citizenship. Once this occurs, then they have the ability to apply for you. Applying involves the same types of forms that the individual with the green card had to go through.
I would recommend seeking an immigration attorney to discuss your options in further detail.
Hope this helps.