A process server keeps coming to our house when we are not home. We have no idea who this is. What will happen if he is njot able to serve us? Can they proceed ?

Eventually yes. There are other forms of service. They will use one. All you will accomplish is delaying the service - the lawsuit will proceed.

You don't need to know who he is - he's a process server. That's the part that is important. In many States after a certain number of attempts it becomes a nail and mail service - nailed to your door and perfected by mailing to your address.

And then you are legally served.

I assume (because you know it's a process server) that he/she is leaving a card - call and make arrangements to be served. Or wait for nail and mail.

You must have an idea who is trying to serve you. It's almost always for a debt.

Actually we live in a gated community so the guard calls my cell when they are at the gate. The guys doesn't leave any info. And the company he tells the guard he works for is not listed

In theory, at least in NY, "he" could serve the guard as a responsible party and THEN do nail and mail - I'm in NY and I own/operate a process service company.