In what concerns to be a Expat in other country and build a social circle from scratch, you can:
- Join a Group/Club/Team
Being an active member of a group is an excellent way to meet people. You'll see the same people on a regular basis. This increases your chance of developing meaningful friendships when living abroad. Local gym, hiking clubs, tennis/ running/ swimming/ yoga/ surfing/ dancing classes, day trips to explore something, working in co-working spaces while meeting people from a wide range of countries, interests, expertise areas, ...
- Take a language class
Language classes are good for meeting other expats. They're also useful for trying to learn a language. Eg. start by initiating once a week lunch after the portuguese class. It would be nice to get to know them better outside of class.
- Connect with other expats through blogs/youtubers/Facebook groups
There are plenty. If you wish to contact some of them, leave comfort zone and start to make the first move to see if they're interested in meeting. There are 50K english people living in Portugal and english speaking expats much more.
Eg.
https://www.expat.com/forum/viewtopic.php?id=895906
There is a wide number of groups that you can join in Portugal that will help any newcomer get situated or for expats looking to make a move to Portugal. Groups to meet new people, make new friends for those who are new in Lisbon, Porto, Braga, Faro, or any other portuguese city.
Meetup.com is a great site for events and meet ups.
You can start a new group here: meetup.com/start/organizing
You can see & join the existing groups and sort by newest/closest/most members/best match:
(You can filter by distance, city). Some of them:
Lisbon Groups:
meetup.com/cities/pt/lisbon/
West Groups (Caldas da Rainha, Nazaré, Peniche):
meetup.com/cities/pt/peniche/
Porto Groups:
meetup.com/cities/pt/porto/
Braga Groups:
meetup.com/cities/pt/braga/
Coimbra Groups:
meetup.com/cities/pt/coimbra/
Aveiro:
meetup.com/cities/pt/aveiro/
Faro:
meetup.com/cities/pt/faro/
Olhão:
meetup.com/cities/pt/olhao/
Portimão:
meetup.com/cities/pt/portimao/
Lagos:
meetup.com/cities/pt/lagos/
Leiria/Tomar:
meetup.com/cities/pt/leiria/
Viseu:
meetup.com/cities/pt/viseu/
Castelo Branco/Fundão:
meetup.com/cities/pt/castelo+branco/
Açores /Ponta Delgada:
meetup.com/cities/pt/ponta+delgada/
Açores/ Angra do Heroismo:
meetup.com/cities/pt/angra/
Madeira/Funchal:
meetup.com/cities/pt/funchal/
Guarda/ Covilhã:
meetup.com/cities/pt/guarda/
Evora:
meetup.com/cities/pt/evora/
(...)