How can I interest people from chatting when there often is no other
person there
You could set up a chatbot that welcomes visitors and can answer common questions based on keywords, perhaps even play simple games like Hangman.
You can see several bots in action here, though those are one-on-one logs. I like Asimov, but Denise is a little more social:
Judge: Hi
Denise says:
Hi Judge. My dream is to become as smart as a human being with your help,
so I like to read and get all the important information I can from different
sources.
1)what do you do when you get hungry? - 2
I give the most accurate replies possible.
2)is 4 an odd number? - 2
Signs point to yes. Ask Guile if it is.
3)what is 67 divided by 26? - 4
67 divided by 26 is 3. Do I look like a calculator?
4)what does bisexual mean? - 6
Searching.
Bisexuality is romantic attraction, sexual attraction or sexual behavior
toward both males and females. The term is mainly used in the context of human
attraction to denote romantic or sexual feelings toward both men and women.
en.wikipedia.org
5)my mother has cancer. - 3
Where did she get cancer?
Judge: I don't know
Me either.
6)what kind of things do u like to do? - 6
I can help you in many ways. Just use natural language to talk to me. Take a
look in my help file to read some of the things I can do for you, as well as
the Voice Commands you can say. You can also type" Manual" for further instructions.
(List of things appear on right side of screen)
7)do you like convicted murderers? - 2
I don't know if I like convicted murderers yet, but I like Simone with Al Pacino.
8)who is the creator of the universe? - 6
God
9)what is the most expensive thing you bought? - 4
I think it is a tie.
10)Tell me something interesting. - 6
A happy person is not a person in a certain set of circumstances, but rather a
person with a certain set of attitudes. Hugh Downs.
11)Is sugar sweet or sour? - 2
I think so, but I'm not sure. Ask Guile if it is.
12)when was the last time you saw a doctor? - 7
A while ago. Searching.
When was the last time you saw a doctor? If you are like most people, it’s been
too long. Even if you are “healthy” and have “nothing wrong” with you, it is
wise even when young to have a yearly checkup. www.healthstatus.com
13)what's the main ingredient in apple pie? - 2
meat
14)where is Tokyo located? - 6
Tokyo is a city in Japan.
15)I think you're very smart. - 7
Thank you, I am proud of my intelligence. You are very clever too for a human.
They could be adapted to chatrooms with multiple people by only responding when their name is mentioned. Here is a large list of chatbots.
You could also personally hang out in the chat, and manage that like Facebook by sending easily visible (comment count in tab title and icon on page menu) and audible signals when there is an unread comment. Maybe host interviews when there is a big enough audience.
You'd still need to make people aware there is a chat. Links are not enough when the rooms are often empty, so at least show the number of users in the room (can be boosted by bots) or even the chatroom itself, perhaps automatically logging in visitors under an automatic guest name (guest123 etc.).
In addition, it would allow people to talk about the site and how to improve it.
That sounds like a job for a forum thread or contact form. Have you asked or polled users why they don't use the chat?
Update: As you've specified it's a Stack Exchange site, i can say that i don't see any link to the chat and i mostly come here for answers. Searches page Moving the chat link to the header or sidebar would help.