It depends on your goal. Are you looking at one particular home that is listed as a pre-foreclosure on a website like Realty Trac? Be aware that many times with Realty Trac postings they are either late or possibly fixed. You see Realty Trac is running off the postings on public records. Many times homes going through a loan modification will appear to be in pre-foreclosure also. If the home is not listed for sale what you are seeing is that many times the homeowners are not really aware of the options open to them. I am a short sale specialist in my area and generally have 7 or 8 short sale listings of my own running all the time.
A licensed Realtor can approach the homeowner if it is not for sale. Now if this is a pre-foreclosure then I definitely suggest that you find a person very well experienced in short sales. We at least know our way through the banks paperwork (which varies with every bank) and their procedures.
If you need some help finding a "short sale specialist" for the area you are looking at just let me know.
Hope this helps,