I suppose you're only referring to unrecognized micronations?
If not - what about Andorra, Monaco, San Marino, Liechtenstein, the Vatican.... even Malta (some people consider it too big).
A micronation, a model country or new country project
With the exception of the vatican all others listed arguably not micronation all have a population above 30k, same as Gibraltar.
Smaller nations are
Palau with over 20,000
Nauru 12,000
Tuvalu 10,000
Recognized, so if a military dictatorship like Thailand give someplace the ok than its legit?
New added
Réunion (unfortunately noting in english)
http://www.reuniao.org/projeto4.0/inicio.htmRepublic of Formoria
http://fomoire.org/Republic of Cascadia
https://zapatopi.net/cascadia/Empire of Atlantium
http://atlantium.org/Texas Nationalist Movement
https://tnm.me/Vermont Republic
http://vermontrepublic.org/vermont-declaration-of-independence/