Do you need an employer to obtain a work visa in Thailand?

I suggest you look at the requirements for a Non-B visa from the thai consulate you're thinking of using.

There are generally two types of visas available to those wishing to work in Thailand. Non-immigrant B visas and non-immigrant O visas. For a non-B a Thai company will have to be involved in applying for the visa, this is not possible to do on your own (a few exceptions apply but not applicable here). This f does not grant you the right to work though, you still need a work permit that the company will also need to apply for on your behalf. For a non-O, you can do it on your own, but you must be married to a Thai and keep a large sum in a Thai bank account prior to applying. This also does not grant you a right to work, a Thai company will apply for a work permit on your behalf. So the sort answer is you can't do any of it on your own, a company will have to hire you before any of this is set in motion.

there is no work visa —- and yes you need a company to invite or sent you to get for example a Non Immigrant B Visa -