Short answer
Moving to another platform should happen only when both people are comfortable and sufficient trust and verification have been established.
Islamic Guidance
What Islam teaches
There is no fixed Islamic requirement to use one communication platform; appropriate boundaries and conduct matter.
Practical Guidance
What you can consider
Avoid rushing. Establish basic identity and matrimonial seriousness first, and protect personal information.
Sources
Qur'an 33:70; Qur'an 24:30-31.