Have you ever opened the lines of communication with coworkers/colleagues and they never respond? What's the best solution to this?

I have to give deadlines when I expect to hear back from them.

I'll set the Outlook email to have a followup reminder pop 12 hrs before I need to hear back from them. Usually give them 2 days. Sometimes I'll flag it as urgent.

If I don't hear back from them within a certain amount of days I will either close their request and note that they need to resubmit it or usually reply back to them asking if they had a chance to review and I'll CC their boss.

Routine greetings is the trend with me and they know am just a door away if they need a listening ear.
Human mind is intricately woven wherein many things keeps going simultaneously. Try not to expect a response and start learning body languages that convey moods many times; focus on essential work affairs.
👍

Probably better to leave well enough alone even though in-house communication is a imperative, too bad they don't understand. If not work related it's not a great idea.

I give them no more than a day or two to respond.

If I can't get a hold of them then, I ask the boss for a hand. 😁

Move on

I appreciate your suggestions. We're better off communicating in person (rather than phone/email).

Just leave it, spend your time more productive😊