If you are a U.S. lawful permanent resident (green card holder), and you have petitioned (filed a Form I-130) for your non-U.S. spouse or children to receive permanent resident status in the U.S. (in other words, an immigrant visa or green card), they would have been placed in category F2A of the visa preference system. As you are likely aware, people in category F2A usually face a wait of between two and five years for a visa to become available to them. The wait develops due to annual limits on the number of visas allotted in category F2A.
If, however, you are facing a wait for your family members to immigrate, it can end quickly if and when you become a U.S. citizen. Your relatives might (under the right circumstances) automatically become what's known as "immediate relatives," eligible for an immigrant visa or green card immediately. (To make sure they will indeed convert to immediate relative status, see How Spouses and Children of Permanent Residents Can Change Visa Category.)
You might think that, because U.S. Citizenship and Immigration Services (USCIS) was the agency to which you applied for U.S. citizenship, and your family's switch to immediate relative status is supposed to be "automatic," USCIS would look at its files and realize that it's time for your family to move forward with the visa or green card application process.
That won't happen, however. The U.S. government won't do anything about this change unless you get in touch and advise it of what should happen next.
In order to advise the U.S. government of your new status as a U.S. citizen, you'll need to provide it with a copy of your U.S. naturalization certificate and your spouse and/or child's I-130 approval notice. How to do so depends on whether the immigrant is overseas, and will thus be consular processing; or in the U.S. and also eligible to use "adjustment of status" as their application procedure.
If the immigrant will be dealing with a U.S. consulate to obtain an immigrant visa for U.S. entry, you need to tell the National Visa Center (NVC)—not USCIS—about your citizenship. Wait until about six weeks after the I-130 is approved by USCIS. By then, it will have sent the file to the NVC.
By the way, now that your spouse and children are immediate relatives, if they are in the United States, they might be eligible to and want to adjust their status. If so, take this opportunity to also tell NVC to send the file back to USCIS so your family can adjust status. Otherwise, because you probably said on the I-130 that they would be applying for a visa at a U.S. consulate, NVC will send your file overseas and expect them to apply for a visa there.
The only way to communicate with NVC is via its Ask NVC web page, which contains a form for you to fill out and submit online. You can attach a copy of the certificate to an email, or await NVC's instructions on how to send a copy of the certificate of naturalization so that it can upgrade your spouse's or child's status to immediate relative. Any mailed correspondence will be destroyed.
Unfortunately, attorneys have found that the Ask NVC line is unreliable when it comes to getting results or an answer. You might need to follow up or hire an attorney for help.
If the case is already at a U.S. consulate when you become a U.S. citizen, notifying the consulate isn't going to speed up your relative's case, but it's important to let the consulate know anyway. The consulate needs to make sure their visa is counted in the correct category.
Call or email your consulate for instructions on how to send your naturalization certificate. It might tell you that your relative should just bring it to the visa interview.
If the immigrant can and plans to "adjust status" (apply for the green card in the U.S., without leaving the country), which is mainly possible for immediate relatives who entered the U.S. lawfully (with inspection by an immigration official), submitting the entire green card application to U.S. Citizenship and Immigration Services (USCIS) will be sufficient.
Include a copy of your naturalization certificate, the I-130 approval notice, and preferably, a cover letter explaining that you have become a U.S. citizen. The process should move forward quickly after that, when USCIS processes the application and calls you in for an interview.
After you let NVC know that you have become a U.S. citizen, NVC will change your spouse's or child's visa category. If you've been corresponding by email, you will get an email confirming that their category has been changed. (You won't get any official Notice of Action receipt in the postal mail telling you this, however.)
The next thing you'll get from NVC is an email telling you it's time for your spouse or child to start applying for the visa, with instructions on how to pay the fees to get the process started. It might take several weeks to get this email. If it takes much longer, contact the NVC. Your spouse or child is an immediate relative now, and there should not be any wait for them to apply for a visa.
If your case was far along and the consulate was the first to hear about your U.S. citizenship, it will take care of the upgrade behind the scenes. If you want to make sure the consulate got it right, your spouse or child should check their visa to make sure the category is shown as IR-1 or CR-1 (spouse of a U.S. citizen) or IR-2 or CR-2 (child of a U.S. citizen). If it's not, the best thing to do is to return the passport to the consulate so it can correct the mistake before the person leaves for the United States. If there's not enough time to do that, your spouse or child should let the immigration agent at the U.S. border know that you became a U.S. citizen—the officer will make sure the correction is made.
You could make your life easier by hiring an experienced immigration attorney to handle your family visa case. The attorney can analyze the facts of your case and spot any potential problems, prepare the paperwork, and monitor the progress toward approval.