Why does a guy go silent all of a sudden?

Before you decide what the silence means, look at what came right before it. If the conversation was going back and forth with questions on both sides and then he stopped mid-thread, that usually points to a busy stretch or a drop in energy on his side. If he gave short replies for a few days, stopped asking you anything, or only answered when you asked a direct question, the interest was already thinning before he disappeared.

Also check the length of the gap. A day or two of quiet with no other signals is normal for most people. Five or more days after a lively exchange is more deliberate, though it still might just be neglect. Look for other cues too: did he stop using emoji, did he change how he signs off, did he avoid plans you suggested. Those small shifts tell you more than the silence alone.

The reply that works here is low stakes and easy to answer. Pick something he said earlier that was actually interesting to you, refer to it in a way that assumes the conversation can continue, and ask one open question about it. A good draft sounds like you were already thinking about the topic, not like you were checking whether he still exists. It should not mention the gap, should not say you hope he is okay, and should not include a second question.

Two other kinds of message fit this moment. One is a plain, warm message with no question, something like a shared observation or a link you think he would enjoy, which lets him respond without owing you an answer. The other is a clear invitation with a specific time and place, which works best if you have already talked about meeting. Both kinds leave out apologies, explanations of why you are reaching out, and anything that reads like a test of whether he still cares.

Send your follow-up during a normal part of his day, usually late morning or early evening, rather than late at night when a message can feel like pressure or like you are bored. Wait at least two full days after your last message before sending anything new. If you already sent one message and got no reply, one follow-up is reasonable, and it should be lighter and shorter than the first.

If that also gets no answer, stop. Do not send a third message, do not post about it, and do not keep checking whether he has been online. Silence after two tries is a clear answer for most people. If he comes back later with a casual message, you can reply warmly and pick the thread up, but you do not need to close the gap by making him explain it. Letting it go is the move that keeps your dignity intact and leaves the door open if he does return.