Hello Trice,
Personally, I've found letters to be ineffective when it comes to soliciting help for a major task of planning a family reunion. Delegate...delegate...delegate. Honestly, if I waited on people to respond to letters when it comes to organizing a committee, I'll have a VERY small committee.

Make a list of 20 family members who you know to be responsible, enthusiastic, dependable, and diligent. Give them a personal call and ask them to be on the committee. Since you've already sent out an introductory letter, they are aware of your plans and the plans for the reunion. If you have a 50% success rate after contacting those 20 people, then you will have a nice, sizable committee of 10 people.

When I planned my very first reunion in 1997, I called on several family members who I knew to be family-oriented and responsible. Luckily, they agreed to help out, and we had about 10 folk at our very first meeting. We planned a great reunion. Now..if I would have sent those same people a letter, I probably would not have gotten a response from most of them.

Just My Thoughts,
Melvin