Let's say your account on Facebook or Wikipedia has been blocked by site administration. Is it a sin, according to Judaism, to create new account in order to evade the block?
I'll assume that the blockage under consideration was the result of violating the site's terms of service and/or that creating a new account to evade the block is itself a violation of the site's terms of service, as one or the other is generally the case when accounts get blocked on websites.
It seems to me that participating in any sort of forum where the identity (account, in this case) under which one is participating is itself a violation of that forum's rules is inherently dishonest. At least as much as they prohibit or justify specific actions, a forum's rules create a sense of expectations shared by everyone who participates. Violating the rules covertly subverts those expectations.
Thus, it seems to me that such participation would constitute geneivat da'at, the overall prohibition against deception.
Here is an excellent survey of the literature on this prohibition, by R' Binyamin Zimmerman at Yeshivat Har Etzion. Here are some pertinent sources among those listed there:
Chulin 94a (with my translation):
דאמר שמואל אסור לגנוב דעת הבריות ואפילו דעתו של עובד כוכבים
As Shmuel said, it is forbidden to deceive people, even idol-worshipers.
Deception is prohibited by the Torah in Leviticus 19:11: "לֹ֖א תִּגְנֹ֑בוּ" - "You (pl.) shall not steal." The unqualified way it's presented indicates that it applies to all kinds of stealing, including deception, and to all kinds of targets.
Tosefta Bava Kama 7:3 (with my translation):
שבעה גנבין הן הראשון שבכולן גונב דעת הבריות
There are seven categories of thieves, and the foremost of all of them is one who deceives people.
Rambam, De'ot 2:6 (with Sefaria translation):
אָסוּר לָאָדָם לְהַנְהִיג עַצְמוֹ בְּדִבְרֵי חֲלָקוֹת וּפִתּוּי. וְלֹא יִהְיֶה אֶחָד בַּפֶּה וְאֶחָד בַּלֵּב אֶלָּא תּוֹכוֹ כְּבָרוֹ וְהָעִנְיָן שֶׁבַּלֵּב הוּא הַדָּבָר שֶׁבַּפֶּה. וְאָסוּר לִגְנֹב דַּעַת הַבְּרִיּוֹת וַאֲפִלּוּ דַּעַת הַנָּכְרִי. ... וַאֲפִלּוּ מִלָּה אַחַת שֶׁל פִּתּוּי וְשֶׁל גְּנֵבַת דַּעַת אָסוּר, אֶלָּא שְׂפַת אֱמֶת וְרוּחַ נָכוֹן וְלֵב טָהוֹר מִכָּל עָמָל וְהַוּוֹת:
It is forbidden for a person to conduct himself with duplicitous and seductive words, and he should not have one thing in the mouth and [another] thing in the heart. Rather, his inside should be like his outside, and the matter that is in his heart should be the matter that is in his mouth. And it is forbidden to deceive (literally, steal the mind) of the creatures, and even to deceive the gentile. ... And even one word of seduction and deceit is forbidden. But rather his language should be true and his spirit should be correct and his heart should be pure from all oppression and tricks.