Learn Spanish (Latin America): No pierdas a ese seguidor.

To tell someone NOT to do something informally (a negative tú command), you cannot just put no in front of the normal present tense. For an -er verb like perder, you swap the ending to -as. Also, perder has a stem change where the e becomes ie, which is kept in this command form. That gives us no pierdas.

Why is there an a before ese seguidor?

This is the personal a. In Spanish, when the direct object of a verb is a specific person, you must put an a right before it. Since a follower is a person you are acting upon, you need the a.

Why use ese instead of eso in this sentence?

The word eso is neutral and used for vague ideas or unknown things. When pointing out a specific masculine noun, like seguidor, you must use the masculine form ese.

Does the word seguidor come from a verb?

Yes, it comes from the verb seguir, which means to follow. Adding the suffix -dor turns a verb into a noun for the person doing the action, just like adding -er in English creates follower from follow.