BJ Gabriel will join Simon & Schuster April 16 as v-p, national accounts. Gabriel, who will report to Rick Richter, president of S&S's sales and distribution division, succeeds David Lappin, who moved to the Popular Group, the start-up being headed by Jack Hoeft (News, March 12). Gabriel is currently director of national accounts at Henry Holt and prior to that had been director of sales for Lorenz Books. She began her career as a sales rep for Prentice Hall and had also served as national accounts manager for the S&S trade division.