I've been a part of the board of TEJO during the last year, the umbrella organization that connects the worldwide Esperanto youth movement. That doesn't mean that is the only organization active in Esperanto, and each national organization has their own organizational structure.
As mentioned in your question, TEJO is an umbrella organisation that connects with national youth organisations. Because of that they have a nice list of national youth organisations on their website which can be used as a starting point.
Some examples from that list that I know to be active are:
- Junulara Esperantista Franca Organizo (JEFO) – French youth
They produce a nice calendar every year.
- Dana Esperanta Junulara Organizo (DEJO) – Danish youth
They recently helped create an Esperanto word game app.
- Junularo Esperantista Brita (JEB) – British youth
They organise a large event in the UK roughly once a year and often have smaller less formal events as well.