Upvote:2
Edited after the comments by Relaxed and Gayot Fow:
- The various Schengen states are taking measures to keep illegal immigrants and people who overstay their visa out. What happens in detail depends on the national laws, but it is unlikely that you will be put on a plane to the US the next morning if you are caught on a ferry. On the other hand, it might end like that if you ignore repeated orders to leave. (@Relaxed, how would you translate e.g. Abschiebung if not as deportation?)
- The Schengen states have a common database, the Schengen Information System. A negative entry from any of the Schengen states would make future applications more difficult.
- When you make an application for a new visa, you will be asked where you live and what your legal status is. Since you are not a legal resident where you live right now, you can't easily apply from Greece. Much easier if you were to apply from New York or San Francisco.
- If and when you apply for new visa or residence permits, it is a very bad idea to lie about facts in the database. If you are found out, your credibility will be damaged.
- You feel persecuted in your homeland due to your sexual identity. You could apply for political asylum in the EU, but I consider it very unlikely that you will get refugee status.
For details about long-term visa and residence permits, ask Expatriates Stack Exchange.
My advice: If you want to live much of the rest of your life in Greece, get home now and apply for a long-term visa from somewhere in the US. You might be able to overcome four months overstay as an 18-year-old if you left on your own, before you were found out.