Most first messages die because they don't ask anything back. Opening with just hey usually gets a one-word hey in return, then silence. A better opener points at something specific — a shared interest, a mutual friend, or a genuine question about their profile.
Once a reply comes in, build on it instead of jumping to a new topic. Ask a follow-up before introducing something else. Conversations grow from one thread pulled further, not from a list of unrelated questions fired one after another.
And don't read too much into a slow reply. Most people aren't ignoring you, they're just living a life outside the chat window. A good opener plants the seed — the rest grows at its own pace.