You have to set the pace by sending them messages regularly. Your messages should also not always be related to SFI. Be genuinely interested in them and other aspects of their lives so that they will not think it is only because of SFI that you want to engage them in conversation.
Tell them a little about yourself, what you have gained from SFI and what they also stand to gain. It would make them open up more to you and get in touch regularly.
All the best!
