My son is to be deported for a criminal conviction, he is a legal resident,I am a naturalized US citizen before he was 18.

One of many requirements for children under 18 to become US citizens because their parents become US citizens is that the children are living in the legal and physical custody of the citizen parents. Was your son in your legal custody at the time you became a US citizen?

Also important is in what year you became a US citizen. The law of the automatic acquisition of US citizenship changed in the last few years. Under the statutes before the current ones, both parents would have to be US citizens if the child was living with both parents. The law as it existed when your son claims to gain US citizenship is likely the controlling law.

What you should do is to let the attorney helping your son know right away about the issue. The attorney will research whether your son is a US citizen. US citizens cannot be deported from the US. If your son does not have an attorney now, you can retain an attorney on his behalf.

Alternatively, there are some groups that provide immigration help for low or no cost. Depending on your son's particular issues, those groups may be willing to help.

If I were in your shoes, I would find an immigration attorney right away. I am in Los Angeles, but I strongly reccomend that you find someone in your local area as this sounds urgent and may require a lot of local footwork.