The retweet function on Twitter allows you to repost someone's tweet to your own followers with a single click. The entire tweet appears to your followers as the original poster tweeted it, including the person's username, with a "Retweeted by [your username]" sign above it. This is an effective, quick way of passing along useful content on Twitter. However, the official Twitter for Facebook app does not cross-post retweets if you use the retweet function. If you'd like a retweet to repost on Facebook automatically, you can use the Selective Tweets app. You must then manually retweet the post and add the Selective Tweets hashtag at the end of the tweet.
Log in to your Facebook account and click the search field at the top of the page.
Type "Selective Tweets" in the search field and click the app link that appears.
Type your Twitter username in the field in the "The One and Only Step" section, then click the "Save" Button.
Visit twitter.com and log in to your Twitter account.
Copy the entire tweet you want to retweet and repost on Facebook, and make a note of the username that posted the original tweet.
Type "RT @[username]" in the field under "What's Happening?" at the top of the Twitter homepage while logged in, where "[username]" is the person who originally posted the tweet you'd like to retweet.
Paste the tweet after "RT @[username]."
Add the hashtag "#fb" at the end of the retweet. This is the hashtag that signals the Selective Tweets Facebook app to repost your tweet on your Facebook Wall.
Click the "Tweet" button in the lower right corner of the "What's Happening?" section to post your retweet to your Twitter and your Facebook.
Because adding the hashtag and retweet information adds extra characters to your tweet, you may need to truncate some words in the original tweet to make the retweet fit within Twitter's 140-character limit. You can change "and" to "&," shorten "with" to "w/" and other similar abbreviations to shorten the character count without changing the original meaning of the tweet. Twitter keeps a character count for you in the lower right corner below the tweet field.