it's important to find a balance that is not too intrusive to others, but which still enables you to get your work done. That usually means using your less preferred communication methods to ask for help, but demanding your preferred methods when people ask for help from you.
No response to an IM usually means one of Too busy, or nothing to say in response, or just not interested in that conversation.
Also, IMs are very intrusive. If I'm typing, or working on something, there is a good chance the window will pop up and steal keyboard focus. Then I'm just pissed off that the person stole my keyboard if it's not vaguely important to me. If it does not need immediate response, then email is best, because that has a built in FIFO style and can be addressed later.
If I'm a worker bee, my own work takes precedence. Helping others is second. Stealing focus is frustrating and will put you at the bottom of the queue, especially for people who are only employed because they have people to help them with every little detail. The problem is that competent people can still have efficiency and self-reliance crushed by a poor organization.
The general order of communication intrusiveness is:
* Phone Call - Immediate response would greatly benefit. Can be responded to while otherwise visually busy. Very limited log of conversation to refer back to later though, which is a negative.
* SMS - Quick response, but limited log of conversation which is a negative. Good for meeting interruptions. Less obtrusive than a phone call.
* IM - Detailed response. Decent log of conversation. Can click links, and maybe even send files. Steals focus and is presumptuous because of that.
* Chat Room - Can be good. IRC style, with name alerts can be handy. Good logging. Difficult to follow if a lot of subscribers. Good for low priority information that can be followed up later. Good for group communication. Low obtrusiveness because you can safely ignore it for a while.
* Email - Most detail in communication. Less realtime than IM. Less demanding. Less interruption of workload. Does not imply "I am more important than whatever you are doing." Great for things needing a response in the 4-72 hour range. Can be overwhelming in a very busy environment.
* Ticket system - Good substitute for email if there are multiple workers and multiple inputs. Can be adapted to support any of the above communication systems. Great tracking of info. Good for 1 hour to 30 day responses. If not all work comes through here, it often ends up ignored. Single input for workflow is important for busy task processors.