This paper makes use of multiplicative vector fields on Lie groupoids to model infinitesimal symmetries of S 1 -bundle gerbes. It is shown that a connective structure on a bundle gerbe gives rise to a natural horizontal lift of multiplicative vector fields to the bundle gerbe, and that the 3-curvature presents the obstruction to the horizontal lift being a morphism of Lie 2-algebras. Connectionpreserving multiplicative vector fields on a bundle gerbe with connective structure are shown to inherit a natural Lie 2-algebra structure; moreover, this Lie 2-algebra is quasi-isomorphic to the Poisson-Lie 2-algebra of the 2-plectic base manifold (M, χ), where χ is the 3-curvature of the connective structure. As an application of this result, we give an analogue of a formula of Kostant in the 2-plectic and quasi-Hamiltonian context.