For informal communication with (some of) the LAMMPS developers you may ask to join the LAMMPS developers on Slack at https://lammps.slack.com
This slack work space is by invitation only. Thus for access, please send an e-mail to "slack at lammps.org", and explain what part of LAMMPS you are working on.
Also note that the slack channel is only for discussions related to LAMMPS development, *not* for people looking for help with compiling, installing, or using LAMMPS. For those purposes, please post a message to the LAMMPS mail list, by sending an email to "lammps-users at lists.sourceforge.net". More info about the mail list is here.
There is also an IRC channel for LAMMPS users which anyone can join.