Should you message them after they don't respond? Usually once, then stop

Before you decide what to send, look at the shape of the conversation. Was the last exchange warm, with questions back and forth and a plan on the table? Or did it fade on its own, with short replies and no hooks? A gap after a lively exchange is usually logistics. They had a busy day, the app got buried, or they meant to answer properly and never got to it. A gap after a thin exchange is more likely lukewarm interest, and that's worth knowing before you spend effort on it.

Also check who's been doing the work. If you've sent the last three messages and they've only ever answered, the silence is partly a pattern, not a single event. In that case a follow-up tests whether the effort is mutual, not just nudges them. Count the gap in days, not hours. Two days of silence after a good chat is normal. Four days after you asked a direct question they never addressed is a different read.

A follow-up works when it lowers the cost of replying. Reference the last real thing you talked about, or offer one specific, easy choice: a time, a place, a yes or no. A question with two clear options is far easier to answer than an open question about how their week went. If you were trying to make a plan, bring it back up with a date attached so they only have to say yes or suggest another time.

The follow-up should carry no judgement about the gap. Don't mention how long it's been, don't joke about being left on read, and don't explain why you're writing. Keep the tone the same as your earlier messages. If the earlier chat was playful, stay playful. If it was calm and direct, stay calm and direct. A message that sounds like the same person as before lands far better than one that sounds like a new, hurt version of them.

Send at most one follow-up, and wait at least a day before sending it unless the conversation was about a time-sensitive plan. If the plan was for tonight or tomorrow, a same-day check-in is fair. Otherwise give them a full day or two. Most people who simply got distracted will reply to a single well-judged message within a day.

If there's still no answer after that, stop. Don't send a third message to see if they're okay, and don't try a different app or a different tone. Silence after one clear follow-up is an answer, even an unpleasant one. Let the conversation sit. If they come back later with a normal message, you can reply normally. If they don't, you've lost very little by not chasing, and you keep your dignity and your time.