Is it better to use a pseudonym when proselytizing on social media to avoid ostentation, or to continue using one's real name?

The fundamental principle concerning righteous deeds is their concealment, as this is more conducive to sincerity (ikhlas (definition)) and further removed from ostentation (riya'). This is unless there is an overriding benefit in their disclosure.

Thus, if calling to Allah using a pseudonym achieves the intended purpose and serves the same benefit as calling by one's real name, then the pseudonym is preferable.

However, if one's real name is more likely to benefit people and garner their attention, then it is preferable to use it, in order to realize this benefit, while diligently striving against one's ego to maintain sincerity and avoid ostentation.