One good place to start is to suggest that they study some of the facts about the real history of Mormonism. Joseph Smith really was a polygamist who was tricked into translating the kinderhook plates and delivered a totally false translation of the papyri of the Pearl of great price (mormon so called scripture). Also almost all of his prophecies contained in the Doctrine and Covenants (also so called mormon scripture) failed. Easily proving him to be just another false prophet. All of these issues are easily accessed on the web and are proving to be devastating to the growth of Mormonism… For example:
”The LDS church Newspaper Deseret Morning News Published: Thursday, Feb. 14, 2008 reported: “Late President Gordon B. Hinckley once told the Quorum of the Twelve, “Brethren, when my life is finished and the final services are concluding, I am going to rise up as I go by, look each of you in the eye and say, 'How are we doing on retention?”’ Retention has become a real focus. For you don’t need an abacus to know many members have left the building.
What happened to them?”
In the United States, Mormons are departing from the faith as fast as converts are joining. Converts rarely remain active in the Mormon Church. The official Mormon reaction to the articles stating that there are significantly less than 12 million members worldwide.
This is from a Salt Lake Tribune article Sep. 1st, 2005 quoting Merrill Bateman, a Mormon Seventy
“…He agreed the LDS Church’s worldwide membership, reported at 12 million, includes many who no longer consider themselves Mormon, but he disagreed with researchers who estimated active Mormons equal only 4 million.
Point: do not be afraid to aggressively help your friends see the truth about Mormonism. Many have left and many more will leave, it is only a matter of someone telling the truth to those who are honest enough to hear it.