Solution

Use TouchableOpacity, Image and Styles.

Key codes

import React, { Component } from 'react';
import {    
    Image,
    StyleSheet,   
    TouchableOpacity,
} from 'react-native';

<TouchableOpacity 
   style={styles.sharebutton} 
   onPress={() => {this.onShare(SHARE_TO_WXTIMELINE)}}
>
    <Image
        source={require('./res/img/wxtimeline.png')}
    />
</TouchableOpacity>         

No Image, No Truth

See Full sample codes Share to WeXin via Modal