When do I worry about missing tenant?

[Jennifer Streamer]

Hi all,  I hope someone has some good suggestions for a possibly missing tenant situation.  We have a tenant who moved in just before May 1st.  We did lots of due diligence - past landlords, personal references, confirmed his employment.  Everything seemed great.  He's a single man in his 50's and a CPA.  He's on the company website and it's a verifiable company.

He paid his security deposit and first months rent and then moved in.  He bought some new furniture and did some work in the yard.  He seemed to be settling in well.

Last Wednesday, I texted him a reminder to include his move in checklist with his rent.  If he had already mailed a check, I said we'd stop by on Saturday to pick up the checklist.  He replied that he'd call with a good time on Saturday.

The rent didn't arrive on the 1st and when I texted on Saturday about the move in checklist.  I didn't get a reply.

I figured I'd wait until Monday, to see if rent arrived in the mail.  No rent.  I emailed and called but there was no response and the phone went straight to voicemail.  Later, I emailed his work and personal email but did not get a response.

Today (Tuesday), I've called a few times and texted once.  Calls went straight to voicemail and I didn't get a text back.  I called his work and the receptionist said he wasn't in today, but put me through to his voicemail.

My husband stopped by after work.  There was a car in the driveway and a torn screen.  The lawn hasn't been mowed in a week or so, I imagine.  There was minimal mail in the mailbox.

Now it's the 6th, so rent is clearly late, but I'm also concerned about him.  This is a quality neighborhood.  The neighbors are also accountants and nurses.  

Should we go in?  Text 24 hours notice and then go in?  Talk to his company HR to see if he's been at work?  Call his personal references?  Send the late rent letter (we'll do that for sure, today).

Since he's only been with us a little over a month, I don't know his patterns, but we've had to communicate a few times and he's always responded promptly.

Sorry this is so long, but context is important on something like this.  What would you do?

Thanks in advance!