A participant in a profit sharing plan cannot be located and the trustee has contacted the social security admin. to no avail. How much time is required to pass before the participant's account is forfeited assuming that is an option?
Any help is appreciated.

Have you tried the IRS's mail-forwarding service? http://www.irs.gov/retirement/article/0,,id=110106,00.html

Try the Search feature for previous discussion threads on this topic. A good search term might be "missing participant" or "lost participant".