continue to keep in touch with all the members of your team, even if they are inactive, by sending an e-mail at least once a week.
Encourage them, make yourself available, do not give up if you do not receive responses, everyone has their own time, do not forget, however, to reward those who work hard and is actively involved in its business.
Use the "reassignment" tool, it gives one more incentive to move forward to achieve the goals.