Assuming you are intending to apply in the US the requirements are very clear on the Embassy website. No travel tickets are mentioned. Note that it is always possible they might ask for it later during the application, they did for me in the UK, but I did have a ticket (why would you apply for the visa if not intending to travel?)
Required documents to upload in the system (Large and clear JPEG or PDF format) to stay with Thai family residing in Thailand (more than 60 days):
Passport Biodata Page or Travel Document (Must be valid within 6 months from travel date)
Photograph of the applicant, taken within the past six months
Document indicating current location (driving license, bank statement, or proof of stay)
Recent bank statement showing the applicant's name and ending balance of no less than $15,000 or proof of monthly income of not less than $1,500/month) along with the current bank statement showing incoming income
Personal details of a family in Thailand, e.g. valid Thai ID card or Thai Passport
Proof of relationship to a family in Thailand (immediate family only), e.g. A copy of marriage certificate / birth certificate / certificate of adoption