Why Do My Facebook Friends Disappear and Then Reappear?
Facebook members can connect with friends in real-time using the social network's Chat feature. With the proper privacy settings, members appear in their friends' Chat boxes when they're signed in. Click on a name or picture from a list of available friends and use the pop-up box to send messages to each other. The "Friends On Chat" list is continuously updated as friends sign in and out.
Friends On Chat
You can see a list of your available friends in two spots. The "Friends On Chat" list appears in the left column of your homepage, and the "Chat" box is in the lower-right corner of all pages. These lists, which are continuously updated in real-time, show status symbols next to the names indicating when friends are logged in and available, logged in and inactive or unavailable. Names and status icons disappear and reappear as activity levels and login statuses change.
Hiding Chat Availability
Hiding Chat availability can allow you to browse Facebook undetected, and stay logged in without receiving unwanted Chat messages. Hiding and revealing your Facebook presence is easy, requiring only a few clicks. Sign in to your Facebook account and click the "Chat" box in the lower-right corner of any page. Click "Options" and select "Go Offline" to hide your name from "Friends On Chat" lists. Slide the switch to the "On" or "Off" position to set your Chat availability for friend lists.
Messaging Offline Friends
When a friend's name disappears from one of your Chat availability lists, it's still possible to send a message. You won't be chatting in real-time, so you'll need to wait for them to receive the message and respond. Click the name of the friend on your list and click the "Message" button. Type your message in the space provided on the resulting page, send and await reply. As names reappear in your Chat lists, resume instant chat as desired.
Facebook Chat Icons
It may not be possible to send instant Chat messages to friends whose names appear in your "Friends On Chat" lists. The Chat icon that appears next to each name indicates your friend's actual availability. A green dot represents a friend who is available to send and receive Chat messages. A gray moon represents a friend who may be available to chat, but has been idle. If you send a message to a friend who's unable to chat, you'll receive a Chat box message that your friend is offline. All messages will go to your friend's Inbox until he or she is available again.