The old-school method of management-by-walking-about (MBWA) is hugely effective. Building relationships longitudinally by having a lot of mini touch times with each person.
In this time of virtual team management, the leader needs to do even more of MBWA (albeit virtually). Have a lot of sidebars with each person on the instant messaging platform. There is value in group conversations in a channel or chat room, but 1×1 conversations really help build trust and confidence. A virtual workforce actually affords more opportunity for this (because physical proximity is no longer a limiting factor).
Adapted from a blog post titled "Leading a virtual entrepreneurial team – Part 6. Team cohesiveness and alignment" by Elaine Chen