First, I strongly recommend sending them a demand letter. You can generate one for free on getdispute.com/products/demand-letter and/or pay us a few bucks to mail it.
Second, physically mail the letter to their legal address. The mail goes to someone in legal tasked with reading the mail.
90% of our cases end here. A correctly written demand letter, sent by physical mail usually gets noticed and resolved very quickly.
If nothing happens after a few weeks (give it 3-4 wks) then you could file a case in court. This will require you to file the case, pay the filing fee, and then serve the defendant via a 3rd party process server. Could all be done in 1 day if you know what you're doing. If you serve the defendant (FB) correctly, they are now obligated to show up to court or otherwise risk a default judgement against them that cannot be reversed later.
Another 50-75% of cases end here as most defendants prefer to settle out of court.
If they don't respond, you will need to go to your court date and explain the case to the judge. Usually, without a defendant appearing, the court will grant a default judgement in your favor, assuming the judge decides they do in fact have jurisdiction. To be safe on jurisdiction, file in the county FB does business, or otherwise has a legal entity registered.
All of this said... it's probably not worth the time/money to do more than send a demand letter. It is probably worth your time to send a physical demand letter.
Good luck. 2.7m small claims court cases are filed each year in the US, approx 50% by individuals. So you're in good company.