The # symbol, a hashtag, is used to designate keywords or topics in Tweets or posts. It was created by Twitter users as a way to categorize messages. It is now used across other networks including Facebook, Google+ and Instagram.

Hashtags (#) make it possible to view messages across each social media platform, which include that #tag in the message.

Tweets and other posts may be tagged by putting #tag  (the tag part is what you will select) at any part of the post.  Here is an example:  Try a great #mystery novel today 

People use the hashtag symbol in their Tweet to help them show more easily on social platforms. Large volumes of searches are performed across the world for individual #tags. This allows people who are not connected to see Tweets on a wide range of subjects. #Tags are used extensively for events, politics and TV shows, as well as more general topics.

Hashtags that become popular often become trending topics on Twitter.

If you Tweet or post with a #tag on a public social media account, anyone who searches for that hashtag may find your Tweet. Please don’t over use #tags. No more than two #tags per Tweet, please.

Please also use #tags only on tweets, posts, and messages relevant to the subject.

A list of ten relevant #tags for writers:

#amwriting – for when you are writing – to connect with others writing

#askagent – to ask any literary agent for advice

#books – to designate a book

#eBook – to designate an ebook

#fridayreads – to show a recommended book on any Friday

#mystery – to say your book is a mystery novel

#read – to recommend a read

#romance – to say your book is a romance novel

#suspense – to say your book is a suspense novel

Please use this free #tag search site to see the relative popularity of any #tag and search for similar and perhaps more popular #tags: http://hashtagify.me/