To find new donors, many charities periodically ask board members to share their personal mailing lists or professional contacts. The organization then creates a solicitation letter, and each board member signs all copies sent to his or her contacts.

That’s a big mistake, says Simone Joyaux, a fund-raising consultant and a co-author of Keep Your Donors: The Guide to Better Communications and Stronger Relationships (John Wiley & Sons).

In fact, rounding up board members’ contacts for a mass solicitation amounts to “trespassing on personal and professional relationships” of those trustees, she writes in the book. “Promise that you won’t!”

“Have you ever asked your board members how they feel about asking their friends and colleagues to give money simply because they are friends and colleagues?” Ms. Joyaux continues. “I’ve asked thousands of board members: Mostly they feel uncomfortable.”

What’s more, Ms. Joyaux writes, such appeals generally bring in only a few token gifts that are not motivated by any real interest in the charity’s mission; instead, they are spurred by a desire to do a favor for a friend or colleague and are usually not repeated.

Far better, Ms. Joyaux argues, is asking board members to refer only those people who might have a genuine interest in the charity’s work. The organization, she writes, should then make an effort to learn more about those individuals’ interests and inform them about its work—all of which should be done before any solicitation is made.