Hello, I am currently an HOA Board President. One of the board members (secretary) moved out of the community in the dark of night and abandoned his home. He took with him important documents mainly all board minute’s in addition or board seal.

We have called, emailed and texted only to get no response. I just mailed a certified letter to the address he abandoned. My question is legally, what are our options. Can we do a memorandum to cover or messing minutes and what do you suggest be done about the seal (similar to a notary republic seal)?

You may be able to put a lien on the property depending on your covenants and restrictions and state law. For all the good it will do I know, but ti may cause the guy big problems somewhere down the line.
Were minutes routinely distributed to all members? Maybe another member has a file. If minutes are simply not available (could happen with a fire or flood too) I would try to chronicle the major events as accurately as possible but I don't know how far back you are talking.
If the seal is critical, I would have a new one produced of a radically different design and maybe notify those who rely on the seal that the old one is void.
I am not a lawyer but perhaps the theft of the seal could be pursued by police. Good Luck.

I too am a HOA President, do you have a property manager or management firm? How about a HOA attorney of record. Old copies of minutes aren't going to stop your board from operating and the seal is not as important as you may think. What state are you in? After 24 hours file a missing persons report with the police. At your next BOD meeting announce that you will be taking names of parties interested in being appointed to the BOD until the next regular election. The old BOD can appoint or elect a current member to be your secretary until things settle.

This may even fall under criminal theft laws, you may want to discuss this with the HOA attorney. I would think first a letter from your attorney would be the start