I don't know about your community, but in many communities, official meetings and communications of a homeowners association for multifamily dwellings are regulated. This could include ample notice by writing or mail of official decision making meetings, potential decisions to be made, and then prompt communication of that decision. This must remain your primary channel - the way you have always done it and should be doing it.
However, similar to the circumstances asked in this question about improving communication in a congregation, you are likely dealing with a diversity of folks and the types of communication mediums they like, and are available for.
The goals of these other communication forums should be to communicate information, and potentially encourage feedback and discussion, but these cannot be used for decision making. Your actual official meetings with official notification must be the venue for that.
Another thing about homeowners communities is that some members (residents) often feel a sense of privacy towards their other members. They likely chose to live in that dwelling, but they didn't interview their neighbors before moving in. Because of this, sending out lists with phone numbers and emails or running a Facebook page are not a best primary venue. Some residents will not want to share their main email address or their Facebook profiles with their neighbors.
A few ideas, depending on technical interest and aptitude of your communications committee include:
Weekly or monthly newsletter, printed, that is mailed to each resident. Also post it on a public bulletin board near a frequently used community resource like the mailboxes.
An anonymous mail server - each resident is issued an email address name@ourcommunity which they can forward to their personal email. Its up to them whether they pay attention, but they can otherwise mask their personal contact information.
Protected access communities such as Yahoo Groups, and Google Groups are good, but don't expect 100% participation. And, as I mentioned, its fine for disseminating information, and even collecting feedback, but assume not everyone has read the online discussion. Slack is a good potential here too, but with the same limitations.
When you really need to get information out, tape a notice to everyone's door.
For monthly meetings, you can also experiment with online teleconferencing software. Adobe Connect, Webex, Google Hangout, and other similar services. You need to check with your local regulations as to whether this can constitute counting quorum at decision making meetings. Otherwise, its simply another way to disseminate information and gather feedback.