Looking on the internet deeply has found these results:

I think so too is the most popular phrase on the web.

I think so either 14,100 results on the web	I think so too 14,140,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
He didn't say he thought so. And I haven't said I think so, either." ?Masters Skywalker and Solo with Bhixen. Bhixen was a senior male Togorian Jedi apprentice�... (otherwise DBUS will just start the first one alphabetically I think, so either the KDE4 version or the KF5 version would not work) Well, those are�... Deanna � Yeah I think so, either end of first half or second half of season 6. Spencer � Probably season 7 me thinks. Maybe relationship with Sasha? Probably�... Aug 9, 2015 ... ... faces because relationships are build on emotions and they change, i think. so, either way you do not realize how much different you became�...	Yes, I think so too. Yes, I think so too. I think so too. No, I think so too. I think so too, and quickly. I think so too, dude. Well, I think so too. I think so too. I have become an actress.

I think so either

14,100 results on the web

I think so too

14,140,000 results on the web

More popular!

He didn't say he thought so. And I haven't said I think so, either." ?Masters Skywalker and Solo with Bhixen. Bhixen was a senior male Togorian Jedi apprentice�...
(otherwise DBUS will just start the first one alphabetically I think, so either the KDE4 version or the KF5 version would not work) Well, those are�...
Deanna � Yeah I think so, either end of first half or second half of season 6. Spencer � Probably season 7 me thinks. Maybe relationship with Sasha? Probably�...
Aug 9, 2015 ... ... faces because relationships are build on emotions and they change, i think. so, either way you do not realize how much different you became�...