This is an interesting question. Do you mean legally culpable or morally culpable?
I'd say there are cases where both are true. Legally, things like incitement to violence, murder for hire, or conspiracy are all prosecutable offenses. Here in Canada, it's illegal to advocate genocide or to incite hatred against any 'identifiable group', defined as 'any section of the public distinguished by colour, race, religion, ethnic origin or sexual orientation.' In all those cases, the illegal action is only illegal because of what it is likely to drive others to do - in other words, making person A legally responsible for the actual or potential criminal actions of person B that may result from person A's behaviour.
Morally, I'd say it's even easier to make the case. Yes, ultimately, people are responsible for their own actions, but responsibility can be on the shoulders of multiple people. Someone who drives someone else to do something should share some moral responsibility for it. That doesn't make the person any less responsible for his or her own actions, but it also means that there are other people who share in the blame.
I think we all have the power to effect the lives of those around us, either positively or negatively. Maybe more power than we realize. Sometimes it doesn't take much - a smile, a word of encouragement, a listening ear to a friend - to make a positive difference. And similarly, sometimes it doesn't take much - a word in anger, a slip of the tongue, a spilled secret - to ruin someone's life or to drive them to do something terrible. And I believe we all have the moral responsibility to be aware of our power and to try to use it for good, as much as possible.