First I send a text message just asking if they are okay.  Second I send a little email asking for feedback.  And last but not least I send a hand written thank you for taking the time to meet with me at 123 Address.  

These 3 steps almost always get me some type of response.

Debbie - Call, email, text, any method possible. First I want to make sure they are okay, and that nothing has happened. Then, after about a week of not hearing from them, I may put them back on a drip campaign and leave it be.

Of course this has happened to me a few times, as I am sure it has with most agents. One of those times I found out later that the buyer clients called on a sign in the yard of a home for sale, and they ended up using that listing agent to help them buy the home (double sided deal). The buyers had no idea what they had done (buying the home through the agent who represents the seller), but lesson learned for me. Always get a buyer broker agreement.

Debbie,
They few times it has happened it has been something going on their life. I give them a couple of weeks and then reach out from a point of view of concern about them not a house.

A common situation, when they want to make a change or slow down they will do everything under the sun to avoid us.

Hire an investigator, send in the National Guard, or just move on to clients who are interested in moving forward.

I do what ever I can to find them again including driving to their home

I leave a few voicemails, emails etc. and if no response I'll just put them on an email drip. This rarely happens so when it does, I wont waste much time on it, plenty of cleints that want to work with me.

Don't presume it's YOU. Usually, when this happens, something is wrong in their lives that they don't necessarily want to impart. Maybe their finances aren't what they made us believe, etc.

another reason I became a listing agent early in the game!!!

Other than calling, texting and emailing, not much else.  Though, I will make a note to check in a few months what they may have bought and with whom.  This has on occasion been a nice financial benefit.

Send out the dogs -- sometimes they need to be sniffed out.  

I call or email to ask if anything has gone wrong with the buyers' pursuit of purchasing a home.  I also ask them how I can be of help in any way to get them back interested in finding their new home. I also tell them that now may not be the right time for them to be looking if they are not sure what they want to do.

Debbie Reynolds All you can do is follow up with them and try to resolve any issues they may have with purchasing.

We all have this happen, and I make two, maybe three contacts (email and phone calls), and if no response, wait until they again make contact or put them in the "missing file".

Loyalty? 

Most have patience with agent 3 months and I gave them a bit more.

I do not take them seriously as most are open ended with no schedule or committment.  Our area one needs to have $200K income to be able to afford a modest 940K home at current interest rate. San Mateo County is close to 1/3rd mil income.

Use every method possible to contact them.

I would call, leave message, email and lastly may drive to their home if i thought something was wron.

Eventually (after about 6 contact attempts)  acknowledge that I understand 'life happens," how I admire one aspect of their character or discipline, and  when they are ready we can resume the house finding mission. Then onto the 77 year drip campaign.

I will text, call, email. If no response, I let it be until/if they decide to come back to me. Mostly I try and phrase the message to say I'm worried about them since I haven't heard from them and want to make sure all is ok.

Fortunately haven't encountered this yet!

Ugh. This has happened to me. I was working with a wonderful couple one time. All paperwork was in place. We saw a bunch of homes over a few months and then they disappeared. I did not do as Anna suggested with the handwritten note, but I did call and email to see if they were okay. I don't remember how many times, but they never responded. That was two years ago and I never heard from them again. Sometimes MIA is forever.

We have a HUGE second/third home market and a lot of buyers are in town for a limited amount of time. It is not unusual for them to just disappear-either going back home without a good bye (todays world) or finding something on the internet and calling another agent which is a big problem. 

 From what I've heard  from other agents, they do their best to contact them by phone or email. It sounds as if somebody has gotten cold feet.

Good morning Debbie. Not a good sign, but things happen for a reason. I would call and email, follow up again and if I still don't hear from them, it is usually a time to move on.

I like Anna Hatridge 's resonse. It has worked well for me in the 2 or 3 cases where a buyer has gone MIA> 

Debbie Reynolds if they have EBA with you, they will be back.

If not - simple, keep reaching them out every hour by all modes of communication until they respond!

I give them a call, and send them an email.  I do not pursue them as intently as I should...

Do you have a signed buyer agency agreement in place?

I'll text and email to make sure they are ok? check in. And if they are truly MIA, I will send listings that come up that suits what they were looking for. I don't chase, but I do try to make sure that I didn't do anything to sour the relationship.