Sometimes friends are working on companies that I think other friends…

 ·  Facebook — Archer T. Ships updated his status.  ·  Markdown source

Sometimes friends are working on companies that I think other friends might be interested in investing. However, it's often the case that I haven't worked with the entrepreneur friend in question, so I can't speak to their work abilities (even though I may value them as a friend).

What's the protocol for making such introductions? What do you think is the proper level of due diligence on the part of the introducer?