What's the proper form (formal or informal) to use when speaking to others online?


I should preface this by saying that I'm myself fairly young (a teenager) and
I speak primarily to other young people. While I may not know their exact age,
it's safe to assume they are either teenagers themselves or adults slightly
older than me who have not stated their age. I use Twitter as a platform to
speak to Japanese people, and generally in replying to their posts I'm talking
about media, art, etc. and I'm not trying to say anything particularly
meaningful.

That said, which is the proper way to speak under these circumstances,
formally or informally? On the one hand, I haven't spoken to most of these
people in private before interacting with them, but on the other hand
communication online tends to be in the informal side in some context, so I am
not sure if speaking formally would come across as excessive or on the
contrary, if speaking informally would come off as rude. I see replies to
Tweets in Japanese in both formal and informal form, so is it just a matter of
choice?

To summarize, the use of formal or informal speech in online interactions in
Japanese seems inconsistent to me, so I'm not sure which one I should use.

For example, in response to a post like

> 最近僕は描くことを考えるときに悲しくてなる

which would be a better reply?

> [name]さんの絵が本当に大好きだよ！

or

> [name]さんの絵が本当に好きです。




I don't think you can go wrong if you use the same formality as if you were
talking to them in person.

If it's someone you don't know, then match their politeness level (as they
also don't know you), or just stick to です・ます Japanese, which is also common.

Even if someone is younger than you (with the exception of kids), it is still
common for adults to use polite Japanese until they are much better
acquainted.

Many places online (for example YouTube comments) will have many people using
informal Japanese, but it certainly isn't wrong to use polite Japanese either,
as lots of people also do.

Between teenagers, informal is probably used a lot online.

